My great dane has been whining and not drinking a lot for the past few days what could be wrong with her?

Anything would be a guess. What does the Vet say?

Gastric problems, bloat (susceptible breed), something else.

This has gone on for a few days? The dog is in pain or distress.

Not a lot to go on.
There could be any number of things going on here.
You should get her to the vet.