This is totally not your fault! Even if your child had given her child the virus, it would still not be your fault unless you knowlingly exposed her to it! My own two kids came down with Hand Foot and Mouth disease last spring and I ended up closing my daycare for four days while they recovered...two of my daycare kids caught it anyway and the rest were okay...nobody blamed me for giving it to them...I did everything I could and it could not have been prevented. So I can understand why you are annoyed...I would be too! However, I'd probably just let it go as she is probably overreacting out of the stress of the whole situation and she will likely calm down once her daughter is better and she is back at work.