I remember having a nasty infection as a kid of about 8, ended up in hospital for a couple of weeks.
One of my abiding memories was stuff tasting absolutely rank. So rather than Lucozade it was puss flavoured lucozade which felt like swallowing broken glass. It took months to get over it and put off quite a few foods and drink that my mum tried to feed me. I cannot explain quite how foul everything tasted for a period of months.
Obviously keep in tocuh with your GP, but as long as she keeping hydrated and has enough food to keep a stable-ish weight and activity levels then it might just need time to pass. You probably already do this, but getting her involved in choosing and preparing food might help overcome some of the issues. Get a smoothy maker?