I would recommend that she was heart tested - some bitches do self whelp - but not always it can depend on their lines, most being booked in a couple of days before their due dates for c-sections, sometimes you can loose the bitches under the general anaesthetic and also loose the whole litter too (I've known people loose their bitch & entire litter of puppies).

It's best that she wasn't bred from until she is at least two/three years old - although I wouldn't recommend breeding from her at all, especially if he's new to the breed and has never bred Bulldogs before, it really is best left to the experts as they can be a VERY tricky breed to whelp, sometimes lots of complications