V.F.
The relationship that she is going to have with her dermatologist is going to be ongoing for years. If she is not pleased about how the office schedules visits, then it is worth asking around for a dermatologist that other people like, and trying out a new one. I don't think taking off 3 spots in one visit should be a problem, unless they are really big spots. If that were the case, that should be the logic used, not a scheduling time issue.
I have had 3 malignant melanomas removed and many dysplasitc nevi removed. There has not been a limit to the number of spots removed at any given visit. (They seem to come sorta spread out over time, so probably the most taken off at any one time was 3 - mine have been all over.)
When I started this process (the 1st cancerous one) I went to a highly recommended Dr, who's practice was 2 hours away. After realizing that this is going to be an ongoing relationship - I asked him and others in my area and found someone who is still good, but located much closer. This makes the scheduling and planning for visits SO much easier, and I do not feel that my care has suffered.
More than you asked for, but hopefully that helps. :)