It is still important to give your dog some exercise. In an enclosed garden is fine, but supervised and be on your guard for her trying to escape, or male dogs getting in. Walks on leads should avoid other dogs, so early morning or late at night is best, perhaps in an area you know to be little used. A bit of extra attention or a new toy at home might help, but beware of giving extra treats because of weight gain. Obviously recall training will have to stop, unless you can pursue this in a confined space - even indoors, but you could occupy your dog with other things like sit, stay, lie down, or hiding a toy for her to find and retrieve etc - little and often is the key. Your girl will try to keep herself clean, which is how some owners are caught out, but you should cover her favourite resting places, as blood is difficult to remove. Also once the bleeding has dried up, although around day 10 from the first blood is the optimum time to mate her, she may still be receptive and fertile, so allow 28 days from start to finish. Modern thinking is to have had the dog spayed before its first season and as she could come into season again in as little as 3 months, I’d get her booked into the Vet sooner rather than later.
We only ever had 2 bitches, loved them to bits, but a nightmare to manage in kennels. Both had litters, then were spayed.