I don't think your being "precious" it's totally reasonable to expect good manners from a guest in your house. having said that...
I'm a very shy person too, I often want to say thank you for something, but I feel I have to wait for the right moment to do so and then it's too late and I can't make myself do it. I'm quite simply afraid to. I never mean to be rude or ungrateful but it's very hard for me to overcome those feelings and I feel horrible for not expressing my gratitude.
I mentioned it the other day to DP and he made me do it there and then even though it was hours later. Maybe she just needs a nudge in the right direction...

Although, if she was giving you nasty looks then maybe it is just plain rudeness in which case I think your totally right in telling her she must be polite or don't come back.