Someone's roo ate a hair elastic and lived. And another found a quarter that was hardly recognizable in their chicken's belly when they culled it. Stomach acid is pretty strong stuff I would say. The thread was on here a while ago if you'd like to read more.
I would think a cherry pit would be no big deal at all. She'll be fine! Chickens eat things like broken glass and all kinds of weird things. Just make sure she has grit and I'm sure she'll be fine.