The only thing I can come up with is if she has had a bath or gotten the area of the frontline wet within the last 5 days. My vet has told me that if the area gets wet the treatment is voided out. Thus why no baths for Mister when he gets his. Other then that it hasnt happened here. And I cant think of any other reasons why its wouldnt have worked. Hope she is ok and maybe your vet has more answers. I would just call and ask. Oh and thanks for the nice lovies you sent me. I feel your husbands pain they did both mine yesterday and I am hurting....