In my honest opinion once she signs the papers in the court house for your hubby to have legal guardianship/custody of his daughter the mom will become a less important part of all you lives. The attorney should order support at this time based on minimum wages. If she is unemployed the court may allow her to take a "break" from child support to help her get on her feet. Getting a job and getting housing is important and after the mom gets those things going then they will reestablish the child support and can deduct it out of her paychecks.
We are raising 2 out of 7 grandkids. One of our 2 dads is set at minimum wage is $168 a month, he is "usually unemployed" and we get nothing most of the year from him. The other dad, K's dad, makes more money so his is higher, and he pays every month like clockwork. My daughter is court ordered to pay child support for both kids I have of hers and she is to pay the same minimum wage amount of $168 for each child. She has been homeless, drugged up, pregnant, and unemployed most of her adult life and is currently in rehab with baby #7. She has never paid a penny of child support in 6 years.
I do not think the girl needs to go to courthouse for the filing of the papers. The judge will want to talk to both parties (mom and dad) about the order for custody so it will need to be done in the court house in front of a judge. That's just not a good place to visit and say bye to mom. They need an informal place that they can have fun and be stress free. This situation will make it much easier on the girl.
Poor thing, it must really be hard on her knowing she won't be seeing her mom every day. Sounds like the mom is having her share of a bad time too though. I am glad she sees the importance of letting her child be in a safe place that she will be well loved.