Ghost Through The Mirror?

Karen was in the bathroom taking a shower. There was nothing on the mirror before she started her shower. she heard a weird noise on glass and after her shower there was a smiley face on the bathroom mirror. She wiped the mirror off and the face was still there. she came downstairs and told me about this and I went up to look and there was nothing on the mirror at all. My thought on this is, maybe it was a ghost looking through the mirror, reason for it not being able to be wiped off and then it mysteriously disappearing.