Hi Rebecca,
I’d like to add that, all the years I’ve dealt with this rare disease, either personally or with others here, I’ve found that any good, reputable doctor ALWAYS welcomes a second opinion, especially from an expert. A second opinion guarantees it’s the patient’s best interest they have at heart, not any ego or pride thing, or experimental approach going on.
In my family’s case, I’ll never forget this… they were talking personally with the head of the neurological dept at a leading university hospital, about getting a second opinion with Dr. Steinberg, and he said,
“If it were my daughter, that’s what I’d do”. I’ll never forget that. He was the best in neurosurgery we have here, yet he knew they didn’t have the experience Dr. Steinberg did, and welcomed his expert opinion. Ya gotta respect that. He was, IMO, a good man and great doctor.
If your doctor is correct in his approach and experienced with MM, than who knows, Dr. Steinberg may agree with him, if he’s not as experienced, it may save her life. That’s how important a second opinion is, in a world where so many in the medical field know so little about this disease. It's very wise to get a second opinion.

Good Luck! Keeping you and your niece in my prayers.
Mar