In this sentence it has the same meaning as 'yet' She is sleeping and only in the next few hours will she wake up.

"Still" usually means that something is continuing. For example: He has been playing guitar for three hours, and he is playing still! So "still" in your sentence means that she is going to continue to sleep for a longer time. The closest word in meaning to "still" for this sentence would be "more." "She probably won't be up for a couple more hours."

Thank you

as in "not yet"

not exactly, it's more like an idiom, and the meaning maybe is IiiiSH :p