I'm going to bed in a moment, but I have to say this first.
Your daughter has made allegations about your husband to the school nurse.
She has taken them seriously.
She has called the Police.
The police have interviewed her and are taking her seriously.
You have indicated to your daughter that you don't believe her 100%.
You have said that you don't really want him to go to prison as you think that losing his family is punishment enough.
On the back of this, your daughter is now thinking of dropping charges, YET insisting that her testimony be kept on file.
Do you not think that she is doing this because she thinks that is protecting you, and that is what you want.
She shouldn't be protecting you.
You're her mother. You should be protecting her. Even if you're not 100% sure then pretend! Tell her you believe her and tell her that it's right to press charges. You should be wrapping her up in your arms and making her feel safe. She should be your priority. Her welfare and her mental health. What she needs should come first, not your concerns about your husband being sent to prison.
FFS! (That means For Fuck Sake)