
Brachycephalic breeds like this are always at a higher risk when under anaesthetic than their longer-muzzled fellows. Having said that, vets are aware of this and take extra-special care that they are 'under' for as short a time as possible.
I have never heard that cancer of the womb is a particularly big risk for bitches - the more common womb trouble they may get is pyometra - pus in the womb - which is a life-threatening condition. Prophylactic spaying is usually done to prevent this condition, and also to lessen the likelihood of the bitch developing mammary tumours. However latest reports suggest that unless the bitch is spayed before her third season there is no such reduction.
After spaying some bitches have a tendency to put on weight - others don't, and there's no way of telling which it will be beforehand!
If you can cope okay with her seasons it makes the decision really difficult for you.
Hope this helps :)