I think that if she'd gotten into warfarin poison at your folks, she'd have shown symptoms sooner, Kally.
I have seen a dark discoloration of the skin on the upper snout before--Ridge had a bad case of folliculitis a few years back and that's how it started. But I don't recall that through the whole ordeal she ever lost her appetite or had any digestive difficulties.
Hope you got in touch with the vet and they had some good advice for you! Keep us posted, pls!