Remember the conditions.

Vauquier has some small thing which she must hide, and which she wishes to hide in Mlle.

Celie's room.

For she admitted that it was her suggestion that she should look through mademoiselle's wardrobe.

For what reason does she choose the girl's room, except that if the thing were discovered that would be the natural place for it?
It is, then, something belonging to Mlle.Celie.There was a second condition we laid down.