Don't forget that pureed carrots also make an amazing sauce. Think of
things they use on seafood and they're usually delicious.
Don't forget "green" sauces. Pureed spinach with herbs, and quick, <shhhh>
tofu cream sauces.
Nightshade allergies are bad, so check with your friend on other things in
that family. I think bell peppers are also of that ilk, as are some other
root thing I can't bring to mind. Pimentos?
I hope this helps!