I would do a search for PKU and see if you can find a good website to guide you through the basics but basically PKU is a disease that is not life threatening but if not treated can cause lots of different brain issues. If not treated as a child it can cause brain delays and problems with development and as an adult can cause mood swings, aggression and problems concentrating (memory loss) etc. She is not going to just die- even if she was to have something high PHE. Almost all food has fat, sugar and protein and the trick is to figure out how much PHE (an amino acid in protein) is in each type of food and what your range is. Bannannas for example have a lot more PHE than apples which have almost nothing. Potatoes have a greater amount of PHE than some other veggies BUT…it is all about how much PHE each person can have and what they choose to fill up on. It is sort of like weight watchers point system- everything has a PHE point value and if you eat high PHE food then you can only have very little of it but if you eat lower PHE you can have more. Every individual also has their own PHE idea intake per day. Some are 150mg of PHE and others might be 700mg of PHe so it really depends. But all in all lower phe intake = better.
And you don't have to worry about contracting the disease – it is a metabolic genetic disease so you are born with it or you are not- and if your mom has it and you don't then you are a carrier. Which means your kiddos might have it if you marry another Carrier or someone who has PKU – but even then it is not guarenteed. If you marry another carrier you have a 1 in 4 chance of having PKU babies.