Hi,
If you actually witnessed your girl "standing" for your male then it's a pretty safe bet that not only have they done it several times when you weren't looking but that you can expect a litter of pups in 58 to 65 days. A female will NOT stand for a male unless she is ready to breed. I am sending you several links that discuss canine pregnancy and whelping.
http://www.pets.ca/articles/article-dogpregnant.htm
http://www.gundogsonline.com/ArticleServer.asp?strArticleID=CC9C3152-813B-11D6-9BF8-00D0B74D6C6A
I hope this helps. Please let me know if you need additional information.
Rescue & Kennel Owner
many years of dogs & cats, current work is with special needs dogs (blind & deaf) & Great Danes