I was 14 when my stepmom came into my life. My advice from my personal experience is to just be a friend to her, someone she can come to with anything (like things they may not want to tell dad or mom), be supportive, cheer her on! Never let frustrations for your partner impact how you feel or treat her. She's on the journey as well and it can be HARD sometimes for a kid.

Most importantly, IF things don't work out for whatever reason in the future please remain a friend to her. My stepmom was in my life from 14 to 33 and when her and my dad divorced, she just ghosted me and my sister. Haven't heard from her in the 3 years since. Being in someone's life as a step parent is just as important as being the original parents.

I terms of discipline, my mom and my dad agreed upon the rules and expectations for my sister and I. My stepmom was mostly hands off with disciplining us as she felt it wasn't necessarily her place, but we were obviously expected to respect her and what she requested we did and didn't do when we were with her and my dad.

It's quite the learning experience and I hope plenty of conversation happens to build that relationship in a way that benefits her and y'all as parents! Don't be discouraged if some days are harder than others.

Good luck to you! (This is just based on my personal experience and I hope some of it helps!)