Ok, first off, let's clear one thing up here...
http://www.pethealthnetwork.com/cat-hea ... oning-catsIf you notice that someone has brought some lilies into your house, you have my permission to panic. Get rid of them right away! Then educate the person who brought them in. They are not just poisonous to cats, they are deadly poisonous to cats (depending on the variety)!
Also, I'm a little surprised that you'd be letting your cat outside under these circumstances? Isn't it possible that this was caused by something she ran into while outside?
Anyway, what has your vet said to you? It sounds like from his actions he is suspecting your kitty might have ingested some sort of foreign object? Either that or some kind of poisoning? Did you get x-rays to verify this? Definitely ask a lot of questions of the vet, and if you don't feel like there is enough urgency there, or your vet isn't taking this seriously enough, get a second opinion.
Let us know how this goes, I'm worried about your kitty.