There is another plant next to the one that makes your balls big that can get rid of it. If that doesn't work, you should be able to use the masturbate emote to get rid of her big balls.
If they doesn't go away after masturnation, it's a bug. Is your save from before the removal of the cow girl or not? Because I had one and it was the only one I couldn't get rid of.
All goods, ended up getting new items i hadnt seen in the "big balls" play through 🤣, also you've done well with this game 🤙 reminds me of old school side scrolling games back in the day