3year old child diagnosed with ALL but now is changed to ABl(AML+ALL)is it possible?

I have a niece whose name is Baran. About 11 month ago exactly in her 2 years old birthday she was diagnosed with ALL. Her doctor started chemotherapy that was helpful and her BM (bone marrow) got normal and she was in her 5th phase of treatment but about  1 month ago, her platelet started reducing again. She had a BM  which shows 11% cancer cells and was considered as a sign of relapse. But her  flow cytometry results were different this time. Now her doctor is confused and thinking that it might be BAL (Acute biphenotypic leukemia) because some factors of AML has showed up this time.and we should start planing the marrow transplant. we are really confused and dont know if it is possible to be cured complitly? and is marrow transplant easy for a 3 year old child? she doesnt have any brother or sister and I am nervouse that is it posibble that her parents bm will be matched with her? I do love Baran she is the cutest and cleverest child I have ever seen. please help me if you have any information about this kind of leukemia. your information of marrow transplant in children will be
appreciated.

p.s. forgive my gramatical problems in english