Advice on custody hearing

Hello! So I have been with my boyfriend for nearly 4 years. We both have a child from previous relationships and now a child together. Since the begining of our relationship, his daughter was always with us. Her mother would drop her off with us any chance she could. About two months into the relationship, his daughters mother had child protective services called on her and her home was deemed unfit for her to live in due to the fact that there was no gas or running water (if was winter). Her mother moved in with her parents (her dad is a registered sex offender who raped his own sister) and my boyfriend did not want his daughter living with that. So she moved in with us and has lived with us ever since.

Flashback two years ago. My boyfriends daughter has been living with us for a year and would see her mom maybe one or two weekends a month, if that. Well her mom ends up getting pregnant with her new boyfriend. She then decided to run away from her new man and move to a brand-new city with her NEW boyfriend who is not the father of her baby. She never told anyone she moved.

One day, she decides she wants to see her daughter and take her "school supply and school clothes shopping". My boyfriend agrees and let's her go. 5pm rolls around and she's no where to be found. 2 hours later we find out she didn't take her shopping. Instead she took her to her new boyfriends house in a new city and she's not bringing her back.

We found his address on Casenet because of course this guy was a criminal, and we drive 45 miles to get her back. Once we get her back we find out that she had to sleep in a twin bed with three other kids (her mom's boyfriends kids) and, in her own words, was too scared to sleep.

After returning home with his daughter, her mother did not get in touch with my boyfriend until 10 months later on her daughter's birthday. After that, every few weeks she will message my boyfriend saying that we kidnapped her (we've never moved or changed phone numbers). She's gotten a DUI and had child protective services remove her new baby from her home because she left her home alone to go drink. Which is when she got the DUI.

My boyfriend got tired of it and we finally had the money to get a lawyer and begin custody proceedings. So that's all been started and in motion. His ex seems to think she will get 50/50 custody and not have to pay child support. Obviously my boyfriend is going for full custody and child support. She seems to be under the impression that our state is a "mother state" and she will get whatever she wants. She is currently going through custody proceedings brought on by her new baby's father because she kept him from his baby for a whole year. Has anyone been in any kind of similar situation?

Sorry it's so long, I just need some advice. It just seems like common sense to us that she would remain here with us and he would get full custody. Rather than divide his daughters time equally between two cities and an irresponsible mother.

EDIT

She also lost her license last month for two years and was also placed on probation for two years.