Hi Allybean, what a worry for you!
As far as food is concerned at the moment, I would say small portions of whatever Saley usually likes - the smellier, the better. It can me more tempting if warmed slightly too. I keep a tin of tuna in spring water with which to tempt mine.
I'm afraid I don't have any suggestions about the constipation, other than trying to include more liquid in the diet (such as mixing a little in with wet food).