I am a vet.
There is a morning after shot. It is an estrogen injection. Will only work if given within 48 hours of breeding. 98% effective
Couple of issues to consider:
1) It will put the female back in the first stages of heat, so even though she has been in heat for 7-10 days, you will have to keep her locked up for another 3 weeks after the shot.
2) 1 in 100 dogs can develop a uterus infection and 95% of those will have to be spayed to get rid of the infection
3) 1 in 1000 dogs can develop a serious bone marrow suppression. I have never seen this in 30 years of practice.
4) It is not recommended if this is a females first heat or it may affect future fertility.
Lastly, if you plan on spaying her anyway, just let her go out of heat and then get her spayed.
txhunter58
venor, ergo sum (I hunt, therefore I am)