Hormones are a big one. If you dopamine give her some deprenyl (good stuff for everyone, even for life extension). NTs are funny & everyone has a dominate NT by nature. If someone is feeling not them self that may be why. Google "Braverman nature test". It's a written test & takes about 15 minutes. It's just an easy first step to see if someone is off. I'd recommend it for anyone.
If someone has NTs that are off that may be (or not) just a symptom of living wrong. Serotonin will really fuck someone up & depression isn't always serotonin. Some "natures way saint john's root" really works.
Of course taking any drug, supp, test or what ever would predicate that one's girl would be open to such stuff. May will tell you to fuck off with your crazy shit cause your not a doc lol. I wont ever hook up with another again that isn't adventurous enough.
Women's shit is more complex. A lot are nuts to start with & they got hormones & men to contend with. Then they get past menopause & about half lose interest in sex.....well that the ones that admit it..........that's when they claim to discover morality & don't want to have casual sex anymore. Ask me how I know that LOL