Well, you are probably not up to dealing with things like a mucusless diet but DAIRY is always a dealbreaker for me from the neck up (and God only knows below that). I stopped drinking milk a long time ago but if I eat ice cream (which I can only do a bit in the summertime), my throat is instantly clogged, etc. My only true vice left (when I was actually able to still eat solid food, that is): chocolate! Of course, I only liked milk chocolate. My sinuses clog up just thinking about it. Of course I've also probably got worms and gallstones and I hope to see many of them soon....
I know there are many decongesting type teas you might want to look into if she likes tea. Warm water with lemon - tasty and refreshing.