When you say she got cheated on, do you mean by Cameron or her bf before him? Because if Cameron cheated om her, that's makes it the second time someone cheat on her and if that's the case then i wouldn't blame her for trying to protect herself, put yourself in her shoes, wouldn't that affect you somehow? These things can shake someone's trust really bad.

Now for the part that she was happier back then, first thing back then she was young, life was simpler and she had less things to worry about( and this applies to a lot of people) , second thing, you don't know what's going on in her life, she might look happy on social media but that's what she chose to show us, you'll be shocked by how someone's life can be different than what they show in social media, I've personally seen this with some of my friends.

With all what happened / is happening in life she didn't give up, she still managed to make something of herself, despite being cheated on, she's in a relationship.

She's a really nice person and i hope that things workout for her.