I'm sorry to hear she diedHate to say I never found out a concrete answer, but papilloma is still a top suspect. The other contender is feathers where they shouldn't be. My poor girl passed away from old age on Sunday so I will never know for sure.
In the intermim, what I gathered since:
-She was having a terrible molt at the time.
-The longest grew in a tight pillar of rings. Some stayed fairly stubby.
-They left pockmarks when they came out. These seemed permanent but weren't raw at all.
-They did eventually come out all at once at the end of her molt! They got weirdly flaky on the outside, not in a powdery fungal way, but like feather caps of all things. You know that particular texture.
-I had accidentally removed one by jostling it and found it had gone from firmly stuck to ready to fall out. So I removed them. No fuss or pain.
-Examining them off her, they were uncannily like pin feathers? That stiff waxiness that gives way under enough pressure.
-She then went some time without them, until this fall when her next molt hit. Just before then they started coming back in the exact same shape in the same pocks.
-They didn't get wacky this time though. they got to a point that matched the original growths from her youth and ceased to grow entirely.
-No change in behavior at any time.
Unfortunately I won't have more information since she is gone now. If anyone else ever sees such a thing again I would be interested in knowing.

Thank you for taking the time to update the thread.