A.H.
My son is 2 yrs old, and had a brief phase of putting things in his nose. It started with a bean one day at lunch time. He has also put a leaf and a raisin up there. There was one more thing, but I can't remember what it was. But, lots of kids do this. And I don't think there's anything you can do to make them stop. It's like them putting things in their mouth when they're babies (dirt, dog food, the remote...) He eventually just stopped doing it. I think it's a phase she just has to get thru.
(I did it once too, a small sea shell. My grandpa had to dig it out with tweezers, and I did not enjoy it. I never did it again).
Good luck!