Nausea after treatment

My daughter just completed a 15 month treatment protocol for medulloblastoma. She was diagnosed at age 13, had surgery to remove the tumor, had 6 weeks of proton radiation, and her major chemo drugs were cytoxin, cisplatin, and vincristine. All through treatment she had very severe nausea and vomiting. She just stopped taking kytril for nausea, but is still on a low dose of decadron to try and control the n/v. It has been 6 weeks since she last had chemo and her post treatment MRI was clear.

Does anyone else have any experience with this prolongeed n/v? The docs do not know why she had it so bad or why it continues. I am at a loss as what to do for her. Any info would bee greatly appreciated!
Sondra