I get it, I don't think there is a wrong way to go. As you mention that she has zero saddle time, then a few rides may be a good idea to help her get a feel for the bike and riding position. If she notices any issues with her back or legs she can then address them with the fitter. She can also ask the fitter about the bike and shifting and other things. But really the gain from a few rides will be minimal and if you just decide to get fitted without riding a few times, no harm there either..