When you say breaking them off, do you mean she is plucking them out or biting them in half thereby breaking them? A possible nervous disorder ??? Is she being beaten up by other birds? Have you watched her do this? Do you have other birds in with her and if so what kinds ? My friend had a rather large and very mean rooster with his and they did not get along at all and finally he got rid of the rooster as it was plucking the pea hens and beating up on them. My females are constantly nipping at my males tail feathers when he spreads, it seems they like the soft tissues or excess skin coating the quills and nip at it and eat it sometimes snapping his feathers and they break and hang. I would have no idea why your bird is breaking her feathers unless she has maybe a lice of sorts? If she is backing up being cornered by another bird or being harrassed by the male it is possible he is responsible for making her back into a corner snapping her feathers, Im sorry Im not much help on this I guess. I have only seen busted feathers on my male or plucked whole ones sometimes more frequently on the females but Ive not seen any of my females break any of their tail feathers ? Do you have a trail cam you could put up to catch what is happening? How large is your pen perhaps more space would help or maybe it is time to separate them ? The literature posted on raising pea fowl I found to be very helpful, there are suggested pen sizes per birds and Ive seen some very cool structures built. There are some very knowledgeable people on here that you could better assist you and also send private messages to for less open chat if you prefer.