Well please stop laughing for a minute and go and separate them until she has finished her season, as a male is sexually mature at 5 months old and she is far too young at 13 months to be bred from. Has she been hip scored or eye tested? And have you studied the pedigrees of the two dogs to see if they are compatible should they be mated?
A bitch can be mated as late as day 32 of her season. Although she will only be receptive for a very few days when she will accept the dog, you have no way of knowing when this time actually is.
I would also point out that there were over 45,000 labs registered by the KC in the past year, and they have been the top breed numerically for many years. With so many being bred, plus all the unregistered ones, do you really think you wil be able to fnd homes for all the puppies or be able to keep them all if you can't?
Please have the bitch spayed between this and the next season, unless you have an extremely good reason for letting her have puppies.