I agree with everything Crayola kiddies said, and another suggestion is to try some pureed veggies, if she will eat pasta with any sort of sauce? or pureed veggies or fruit in homemade banana or zucchini bread, muffins, etc.

You can only do what you can do though. Given that she's already kindergarten age, and her parents don't put a high value on nutrition or healthy food for her, and willingly provide her with junk food instead of what her body needs... it's probably a battle you can't really win, at this point.

The purees in homemade breads/muffins/pasta sauces might help get a bit of nutrition in her, at least.