Hi JJ -
Sentences like that are (I think) the origin of the "don't end a sentence with a preposition" rule, which is without validity in most other situations.
It's a preposition, not an adverb, and it's one sentence in particular that sounds like nails on a chalkboard to me. It's non-standard.
Where is she? Where are you?
Not Where's she at? or "Where're you at?