Hi @LibbyA. I had an MRI bulk billed thru Uniting Care medical imaging at St Andrews hospital in Brisbane. However it was on my spine and not my breasts. I don't know if there are different rules for bulk billing on different areas but you could give them a call and ask.
In regards to her cycle if she has no uterus does she still have her ovaries? Because at her age they are still likely to be releasing oestrogen at various times. I suspect the only way to work this out would be repeated blood tests to measure her hormone levels. And then plan an MRI date from there.