I would say it is better to make sure she is fully mature before breeding her. At a guess, I'd say that was about 2 years old.
But this would also depend on her condition, and whether she is prone to any genetic health problems, in which case, it would only be fair not to breed her, (for the sake of both her and her puppies) and have her spayed.
You could ask the vet to run health checks on her before you think of mating her, to make sure she is not predisposed to any health problems inherent in her breed, and to also make sure she is in first-class condition. Then she will have a happy healthy pregnancy, produce happy healthy puppies, and be ok afterwards.
Also, when the time is right, don't forget to ask about any nutritional needs she would have during pregnancy and motherhood.
Breeding, and ESPECIALLY breeding of dogs like bulldogs (of any kind), is not something to be undertaken lightly.
The breeding of ANY bulldog breeds is expensive since many of them have to be artificially inseminated because their physical structure makes it impossible for them to breed naturally. Artificial insemination can cost upwards of $1500-$2000, just to get the female bred. Then, hopefully, the breeding is successful, you're looking at $2500-$3000 for the Caesarian section surgery to deliver the puppies since the size of their heads often makes it impossible for them to whelp naturally.
You also have to consider the genetic health of your dog before deciding to breed her. In breeds like this, it is more important than in any other breeds to make sure she came from a breeder who is breeding their dogs with the improvement of the breed in mind and not someone who simply bred their pet because they wanted to have a litter of puppies, because there ARE so many health issues with the bulldog breeds. Most serious breeders of these dogs sell their puppies only with spay/neuter clauses on their contracts to ensure that they will not be bred, since breeding them is such a risky thing.
While breeding any dog has its risks, breeding these dogs can be a death sentence for both the mother and the puppies, and at the very least, can end up costing you an arm and a leg to save them. Please consider spaying her instead. If you spay her early, you will virtually eliminate the chances of her developing mammary cancer, and you will COMPLETELY eliminate the chance of her developing pyometra, which is a life-threatening infection of the uterus. If you want another puppy, find a reputable breeder through the French Bulldog Club of America and purchase one, but please don't try to undertake this task yourself. There are too many things that can go wrong with bulldogs.
it is best to wait until she has her second heat i used to work for a vet english bulldogs are the hard ones to breed.by the way your baby is cute cute
French bulldogs have the same issues with breeding and whelping that English bulldogs have. http://www.bullmarketfrogs.com/articles/breedingrisks.htm
Only a very small percentage of French bulldogs can breed and whelp naturally, the rest have the same problems that the English bulldogs have. The website that I put the address up for details the cost of the correct methods of breeding and whelping a litter of French bulldog puppies, and in the nine weeks from conception to whelping by C-section the grand total was $6900plus dollars. They are a very risky dog to breed, and this owner is obviously a very green novice if they don't know how old a dog should be before being bred, so please don't mislead this person into thinking that there are no risks in breeding her dog.