Yes both me and my sister have to drink a formula. My sister drinks something called Phenex 2 unflavored and I drink PKUexpress coolers which is formula that is like a juice that comes already made in something like at juice pouch and I also take Phenex chews which are like little tablets that you can take instead of formula. I actually have 5 sisters and a brother, Amber is 18, Aaron is 16, Cassandra is 12, Danielle is 9, and faith is 5 but they don’t have PKU. Erica is 8 and she has PKU like me and your sister. Erica loves her formula but I have always had huge problems with finding one I like. If you sister is having trouble with her formula maybe your mother could take to her PKU doctor or dietian about trying other formulas. There are alot of things out there besides just drinks, like I know they make phlexy 10 bars which look basically like candy bars, then there are the phenex chews which come in chocolate mint and lemon lime flavors and they are like little tablets that are the size of nickels. Plus alot more.