Thanks @Aunt-Deb!
No school nearby. And I don't know that I want her being cut on by a school for something so sensitive. If she was young and it was more routine, maybe. But I have a couple of options and am going with the one I think will be most likely to succeed, all things being equal. The more expert option is about $4k.
She needs her uterus out anyway, so since they'll have her open we're going for it. They'll see what this mass is and make a decision.
The other option is to do a detailed ultrasound. That costs about $400. But, again, they need to open her anyway, so why bother? It would provide more info, but the cost doesn't seem to provide enough benefit, IMO.
There is some sense of urgency too. We don't know what's going on, and waiting to negotiate may not be best. She's still doing fairly well. I want to give this a shot while I think she still has the strength to endure it and heal well.