Hey Seb, everyone here has already offered great advice.
Just a question, you may have already said but I can't remember....do you have Carol Sinclair's book The IBS Low Starch Diet? I ordered mine at Paper Plus...you can probably also do the same at Whitcoulls or whatever bookstore is near you.
If she reads it (it's a small book) it may help here get a better understanding of the diet.