Lots of ways to deal with her, but an easy way is to be extra rough with her at first, don’t worry about despair, in fact get as much as you can to quickly lower her attributes so she is less resistant, then get her to drink a Lethe potion, and then start over with an easier blank slate.
Low stamina can be solved with supplements and nutritionist rule, vesturian ambrosia, sparring for exercise (she can’t refuse), among others. Obviously once she doesn’t get F- grades from tutors in athletics you can start raising it faster. Don’t forget sneakers and leotard. More energy and better mood also help. Use all the tools at your disposal. Drugs, encouragement, spa, sex, etc… based on the situation.
First what are you doing to lower her stamina, maybe don’t do that so much?
If you want to try upgrading your game to the latest dev build I’d like to know how it goes for you with that. Especially if you use rape or active sex.