since she is clearly trying to have it both ways based on what suits her.
SInce you teach the class why can't you schedule it during your time only?
Seems the best course of action, the one that I would take, is to do what you want on your time and let her do what she wants on yours. If she signs squirt up for baseball on your time, blow it off if kiddo doesn't want to go and find a better alternative for you and your son to engage in. Put the onus on her to take you to court and prove that signing up kiddo for a team sport without consulting you and making him go during your parenting time is more beneficial to the kid than some one on one time with dad fishing at the local lake (or whatever activity you decide).
The court wants parents to work issues out themselves.
Possibly so. So do what you want and make her the problem by taking you to court over petty issues.