Unless your dad sealed off the area that had the mold chances are he's cross contaminated the entire trailer and if your mom is a sever reactor like most of us your dad will never be able to get it clean enough for your mother to regain her health.
That's the problem with mobile homes is their notorious for leaking and your not aware of the leak till its to late and someone has gotten sick. If at all possible talk your dad into getting rid of the trailer and getting into more conventional housing. If it isn't possible and trailer is all they can afford look for an industrial hygienist in your area. Call more than one and ask them about their qualifications and tell him/her about your situation. Whomever you decide to hire have that person go through the potential new mobile home with a fine tooth comb and make absolutely sure there aren't any leaks. Your going to want him to check all the seems and an inferred sensor. Once he writes his report have him/her explain everything in the report. If there's something in the report you don't understand ask him to explain it to you. That's what he's getting paid for