If she's still hungry, feed her more. If she's hungry, it's because she's hungry and she needs more than what you've offered her already and that's perfectly fine. As long as you're not forcing her to eat or she isn't projectile vomiting everywhere after (can often be a sign of reflux, babies who take more than they are hungry for do it to soothe the reflux, but then they can vomit it all up after if it's too much), then you can't possibly overfeed her. She's a growing baby and needs as much as she wants. The hungry milks just have a different type of protein and some fillers in them to trick their stomachs into feeling full when they aren't (kinda like how adults drink fibre drinks when they are trying to diet). But babies don't need to diet. So just keep doing what you're doing and feeding her as much as she wants whenever she wants it, and ignore your MIL's advice.
