I don't think he ripped her off necessarily. He allowed her to experiment with valuable gems without knowing whether she'd be able to pull it off. I also doubt she thinks her reward was insufficient. She wasn't expecting anything in the first place, she just wanted to learn about enchantment because she was curious about the present her husbando gave her.
Though she does need to quickly realize how valuable the things she produces are. Everybody so far (besides the prince) seems appreciate her skills and treats her well, but that may not be the case once the king/military/foreign nations realize what she's capable of.