I'm an idiot. I used the trigger word "Frankie"*. Which, without any other information for Flux to go on produces males. D'oh!

All you need to do is use the term 'woman' or 'female' and it should be fine.

*Before anyone says "Oh, you don't need trigger words, blah blah" - you really do. It's always best to have them to prevent bleed and allow multiple LoRAs. Empirical tests, by people who know far more about this sort of thing (and by me as well), have proven their value.