"Tonic water will work for bitter, and lemon juice or something else acidic for sour. Cranberry juice will do both. But go easy, a little goes a long way." It's easy to add more flavoring if you don't have enough, but if you dump in too much.... There's something else that concerns him, too.

"Assuming you don't have any special dietary requirements?" He can't help but notice that she doesn't seem to be human; that doesn't bother him so much, but he doesn't want to recommend something that will poison her.