"You said this was grape juice!" "I fail to see the problem, dear." I agree. What grape juice is she talking about, and why is the alleged grape juice a problem?
The "grape juice" was/is in the flask on the right. Presumably, it was a potion of some sorts, perhaps one to increase breast size, as the image shows a wardrobe malfunction. Alternatively, it could have just been alcohol (wine is often made from grapes, but hardly comparable to grape juice), as consumption has left a blush on her face.