My chicken is acting odd?

I only have two chickens. One is a BSL and the other BR. The BR is the one with the trouble, and is around 9 months old. She hasn't layed an egg in a week and a half. She has been aggressive towards my BSL for the first time ever in this time. She pecked her legs, and comb, and her top feathers are gone. I don't think it has to do with the weather since they were laying eggs in colder weather than it is now. Last week I didn't have oyster shells for 4 days because the store was out. Could this be the reason why or could she have something like worms? Thanks xox