So sorry to hear your story, I wish you lots of luck
Have you investigating MIBG therapy?
Have you done any genetic testing for ALK, PHOX2B and so on? If she is ALK positive there are some very promising treatments around the corner.
There is a COG clinical trial that attempt to combine immunotherapy drugs with chemotherapy that has had some positive press that may be worth exploring. ANBL1221: A Phase II Randomized Trial of Irinotecan/Temozolomide with Temsirolimus or Chimeric 14.18 Antibody (ch14.18) in Children with Refractory, Relapsed or Progressive Neuroblastoma
It attempt to combine irinotecan, temozolomide and ch14.18.
There are also some other trials available in the US with humanized antibodies at St.Judes and MSKCC but travel and treatment would be enormously expensive.
Wishing you lots and lots of luck!