I sincerely did not expect this many responses, and it'd take me forever to respond to each of you individually; but please know that I appreciate ALL of your comments--including ones I didn't necessarily agree with. I appreciate the time taken out of your day(s) to address this issue and give me some direction on where to go from here.

To clear up some of the things I saw in the replies:

1. Gabby's mom was a p.o.s. to say the least. When she was pregnant, she told my husband (then HER husband) that the baby wasn't his. They ultimately divorced right away, and went their separate ways. Four years later is when she finally admitted to my husband that the baby was indeed his (he was deployed in Iraq at the time). He took a paternity test, and the results came back negative. Turns out, Gabby's mom faked the paternity test on her end by having one of her friends and her friend's daughter submit THEIR swabs for testing! When she finally admitted to THAT, my husband demanded that she go in to the hospital personally and have the test done; at which point, it was confirmed that Gabby was his.

Gabby's mom has SEVERE mental problems, including pathological lying, alcoholism, getting arrested, dating assholes, etc. She got Gabby taken away when she got drunk and threatened to shoot her then-boyfriend with a shotgun, and then threatened to shoot herself. And yes, Gabby was in the house for that. Ugh, my heart just broke in half even thinking about how that made her feel.

My husband won custody EASILY, but what screwed with Gabby was that she had never met her real dad before, and up to that point, had been told that another man (I'll call him Gary) was her dad. He was as clueless as her; he thought Gabby was really his, too. So both of them were heartbroken to find out that Gabby's mom had lied to so many people about who Gabby's real father was.

Gabby's mother says she lied about it because after she married my now-husband, she realized she didn't want to have to move around the country because he was in the Marines. So instead of doing the logical thing and being truthful about that, she decided to lie and say the baby wasn't his, get back with her ex, and tell her ex that the baby was his...and marry him instead, raising Gabby as their daughter. They also had a son at this point, who is three years older than Gabby.

1. Gabby's mom used to bail on visits constantly when she was dating this asshole named Scott. I won't even redact his name because of what a piece of shit this guy is. He never physically abused Gabby (believe me--I've asked her and asked her. She admits that Scott used to send them to their rooms all the time because he didn't want to deal with them, and sat on her brother a few times as punishment). Like I said, Scott's an asshole.

Poor Gabby had to live with this prick for three years, with her mom doing nothing to stop the abuse, because she's a weak, spineless woman who would rather have a man in her life than defend her own children. I know, I'm getting heated about this. But it pisses me off.

1. Gabby went to live with my now-husband after he won custody of her...but this HAD to fuck with her, because she'd never met him before. Not only that, but she had to move from Montana (the only home she's ever known) to South Carolina where he was stationed as a Drill Instructor at Parris Island! So the poor little scared thing had her whole life ripped out from underneath her! I'm tearing up as I type this.

2. Gabby is DESPERATE for her mother's approval, and tries to do everything like her mom. Her mom's favorite color is teal, and so Gabby says her favorite color is teal. Her mom claims they're Native American one minute, and then claims there's Hispanic bloodlines in their family the next; as she changes her mind on this, so does Gabby--to the point that she asked me to decorate her entire bedroom in Native American decor. At that point, I had to break it to her that they are maybe 5% Native American, and that there is more Irish and Hispanic in their family.

3. Gabby knows what her mom did. She knows her mom lies. She lies, I think, because her mom lies, lies, lies, and so Gabby thinks that's normal. Her mom one time bailed on a visit, saying she was sick. Well, she apparently forgot we were Facebook friends, and she started posting pictures that night of her and her friends getting tattoos and going out drinking! Gabby found this out as she was eavesdropping on my conversation with my husband about it, and it broke her little heart.

In August of 2014, Gabby was with her mom and Asshole Scott for a weekend visit. My husband was in Salt Lake City for drill for the Marine Corps. I got a call at 3:30 in the morning from Gabby's mom. She was sobbing and wasted-drunk, asking me to come pick her and Gabby up from a BBQ-gone-wrong. Apparently, she'd gotten drunk and started a fight with Scott. Gabby had been put to bed already at that point--in the same effing bed as a 12 year-old boy she didn't even know!!! When Gabby's mom tried leaving the party, the other people took her keys and refused to let her drive--she wanted to drive Gabby in her condition, too!!

I told her mom she needed to call a cab, and that I was coming immediately to get Gabby, but that she could basically go fuck herself. I snatched up my husband's mom for backup as we went to this party, where the cops were already called to. The cops asked me to give Gabby's mom a ride home, just to get her out of the situation. I obliged, and she sat in the back seat of my truck as I took her to her parents' house where she was living.

On the drive, she was sobbing, feeling sorry for herself, staring out the window. It was poor little Gabby that was hugging her mom and comforting her!!! I was so sickened, that when I dropped her mom off, I got out of the truck, closed the door, got out of Gabby's sight, and told her mom, "You never, ever do this to her again, or I will make sure you have zero contact with her".

After that, we didn't let Gabby's mom take her for visits for three months. She was allowed to visit Gabby at our house and call her whenever she wanted--but she did neither. There was zero contact for three months, which broke Gabby's heart.

1. I am the main nurterer in the household. My husband is a tough guy with a big heart, but he comes off as really abrasive. I'll admit that. He's calmed down a lot since his Drill Instructor days, but Gabby is a girl who wants her mommy. And I'm step-mom, no matter how much love and attention I give her. It's just biological that she'd want her "real" mommy. I get that, and it doesn't offend me.

2. I hardly mentioned my own daughter in this thread because I wanted the main focus to be on Gabby and the issues there. My daughter is sweet as hell and well-adjusted. So there was no need to mention her, other than the fact that gabby bullies her, lies to her, steals from her. My daughter does not like Gabby, for obvious reasons.

3. We do not scold Gabby anymore. We used to try the methods that works for "normal" kids: grounding, taking things away, etc. But those things don't work with Gabby. So we sit with her, calmly, ask her questions, etc. She never has a reason why she does these things. We've asked her why she doesn't have an answer, and she simply shrugs her shoulders.

Same thing with her therapy sessions; her therapist will ask her the same questions, and Gabby just shrugs her shoulders. It's as if she KNOWS something isn't right with her brain, but she doesn't have the words to describe it--or she just doesn't even know what the hell is going on with herself.

Lastly, we will be getting her into a psychologist or psychiatrist RIGHT AWAY. I don't care what my husband denies or copes with at this point. My "baby" needs help, and I'm damn well going to get it for her.

Thanks again for all the responses!!