There are behaviours that are specific to individual breeds, and dogs for that matter, but with my own main breed, there is really no difference between the genders, other than the fact that the male Basset is 'more' - wrinkles, bigger usually and heavier. Obviously the one big difference is the fact that a b itch will come into season roughly twice a year, but the intervals between seasons varies. I'd suggest with the Mastiff, her cycle will probably be closer to 8+ months, than 6 months. Some bitches can get 'moody' when in season, although again, I didn't see this in my girls. But that's easily remedied by getting a b itch spayed by around 6 months!
I have found my girls to be rather more independent than my boys who just want cuddles (don't they all!). But again, each breed is different, and so is each dog within that breed. If you are considering having this b itch, I'd go sit down with her breeder who if she's responsible, and cares where her puppies are going, should be more than willing to discuss all the pros and cons of the breed, including any difference between the genders.
ps I started off with male Bassets, one first and another 10 months later. But this was more about the wrinkles, and the fact I'd never been around a female dog.