I have a bitch and a dog and my bitch has been in seaon for 13 days she has been mated with a dog (not mine) but my dog now will not leave her alone. How long until she is not able to accept penatration?? As I cant leave them at the moment in a room together and my dog will not stop crying/barking??? My bitch's breed is Lhasa Apso

It could easily be another week till she will refuse to stand. Was it a planned mating with another Lhasa? If not, take her to the vet asap for an injection to prevent pregnancy, especially if the dog was larger than her. Is there anyone who will board either your dog or your bitch until she has finished her season? Your dog is likely to become very distressed at her proximity. :(

At least another week ,as she was willing rto stand quite early, but I would watch them crefully for another week after that.