do you have the court info, name of the judge, etc.. that did the custody order?
she doesn't need anything fancy. it will take a little while to do, it isn't something that will be over night.
she needs to sit down and work on a letter to the judge. let her tell the judge her story. why she wants to have the custody changed. that she isn't living in the father's house and that she wants to change it to live with the mother. just let it be her words. then you mail it in to the court house, attn: the circuit clerk or the judge that handled the case.
mark the top with all of the identifying information, such as the case #, names involved and what the letter is about.
you don't necessarily have to copy the father on the letter, but their is the possibility that the court will contact him for an interview.