手術後(癌症)休養期飲食

Sorry to hear that. Hope the operation went well, and by three weeks, she should have her stitches removed. It would be a good occasion to ask your surgeon what she should be eating, not necessarily the type of food, but the texture of the food, solid, semi-solid, minced meat, etc..
Failing that, I would suggest some soft but nutritious food like Tofu, yogourt, rice soup (porridge) with fish, chick soup, etc.
Hope she has a good rehabilitation.