You did the right thing in presenting them with the bill. Since you said you had a good relationship with them I may have done it in person rather than by letter, but the fact that I am older has a lot to do with that (I don't think you should have). However, they should be responsible for the costs associated with the injury caused by their dog. Taz went after a friend's dog while we were talking about a month ago, and I offered to accompany her to the vet or pay the bill (just a little puncture under the eye-she said she would take care of it herself, no vet). They probably didn't realize that Giselle was actually injured at the time. I hope Giselle is feeling better.