There are a number of things that can cause hair loss. Rubbing against crates, xpens, gates will do it. Anything a dog sticks his or her nose up against routinely.
A fungal infection, bug bite, pimple, all kinds of other things can cause hair loss.
How old is she? Did this start recently?
Do you have a photo that isn't as close up? I can't see anything in the photo you posted.
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