Before I go on please know that you will be questioned on your breeding practices if you continue to post on this board.
Many members work in rescue and see awful things. Many don't believe in breeding while dogs are in shelters dying all over the world. Others only believe in responsible breeding which is the category I fall in.

How old are your dogs and is this the first time for both of them? Somtimes when dogs don't know what they are doing they need to be helped.
Talk to your vet or breeder about Artificial Insemination.

I can't imagine that the female is so short that there should be problems. Afterall they are the same breed so the size difference shouldn't be that great. According to the AKC standard dogs are to be approximately 23" and bitches slightly less. So if your bitch is significantly less than she is not within the standard.

I really really hope that both dogs have some kind of titles, and have passed all health clearances, and I don't mean just being checked by a vet and being deemed fit.

Please, unless your dogs are excellant examples of the breed and have many traits to pass on and improve the breed, reconsider breeding until you have done some more research and are more knowledgeable on the subject.