There's more to breeding than having a purebred that's in heat....
Has she been tested for health conditions known to the breed (Prone to hip and elbow dysplasia, PRA and eye disorders)? Is she certified with a reliable kennel registry? Is she up to date on all her vaccinations? Has her temperament been evaluated?
Will the 'stud' you choose, also have all these requirements?
Will you be willing to provide proper medical care for the pups, while they're in your care (should have first round of vaccinations by the time they're 'sold').
These are just SOME of the things that should be looked into, when you think about breeding your pet. If you're going to breed, then do it correctly. Otherwise, spay/neuter and give all the Lab & Lab mixes in shelters, a chance at homes.