What Does It Mean When A Kitten Stops Using Her Tail?

Yes that doesnt sound right at all. The tail is a bone so it could have been damaged in some way. The jumping issue would certainly point to a balance problem as we all know tails are important to their balance. Unfortuantely its only going to be proven by a trip to see an expert. Does she flinch when you touch her tail?

What you should also look for is the possibility of an abscess at the base of her tail. That has happened many times with the strays outside I care for. When they get bitten by another cat (your older male, for example) they get abscesses so easily. I'd have a vet check it out cuz the earlier reply suggested injury since their tails aren't only bone, it's an extension of their spine, hence, poor balance.