There’s certainly no general rule that could apply to everybody concerning sex and music. The fact is that a lot of artists (not only musician), probably the majority of them, have their own affective/love life as their main source for inspiration, that was particularly the case for romantic musicians like Beethoven, Chopin, Liszt, Schumann…
It’s quite obvious that having sex affects your person from one way or another. There are people who get stimulated by some *** while others would be completely “emptied” by an intercourse. It’s clear that if you have sex the whole night before a recital, you’re likely to play crap…, but not only that, the biological process that’s going to take place after having sex, like the production of some hormones, is going to have different effects, depending on the person, as far as concentration, muscular relaxation, perception and so on are concerned.
Playing music and having sex have at least two things in common:
1) you use your body
2) it provides you pleasure, physical as well as mental
The same statement could apply about playing sports.
As far as our physical and affective resources are limited, a lot of *** will absorb some resources that are going to be lost for playing music and inversely, playing a lot of music (for example if you have to prepare a big test, a recital or a recording) is likely to decrease your physical interest for your partner (if not worse: it might even jeopardize your overall interest for the entire person).
Then, it definitely makes sense that Caro plays better when her sexual life is not active. The need for sexual activity (libido) is generally admitted as one basic need of our… mind. Lacking of sexual activity automatically generates a frustration that you need to compensate in a way or another, then, playing music could be a great sublimation, an alternate recognition of your body and an alternate pleasure (there are so many musicians that seem to get almost orgasmic sensations from playing).
The bottom line is that our life needs balance. The ideal would be to have great sex AND play great music. It’s just about allocating resources properly (physical and mental energy, time…) and taking the positive from both in order to use it in the other domain.