
I wouldn't worry, my girl did exactly the same to me 5 weeks ago, she wasn't ready until day 20!!!! after travelling 900 miles back and forth to the stud we ended up having her premate tested at the vets, 3 blood tests later she was ready, so as long as your sure she hasn't gone over then get her tested it will put you mind at ease. My girl had a litter last year, one mating day 11 - 7 healthy pups, completely different this time though!
Good luck!