I agree that it should be something we can discuss maturely, without any personal comments towards people, as this is the way we learn, and for people like me, who have only been doing it a short time, and haven't been in this situation, it is good for us to have a discussion which could help us if we are ever in that situation. I have had 2 mum cats who have been allowed out while kittens were still with them, so potentially could have, and both were spayed regardless, as they were both 10 months old, and had already had one litter. Fortunately neither were.
I think I would have done the same as you Dawn, as she has been through so many litters already, I would be very concerned about her health, and the chance of her being able to give them enough to produce healthy babies - our first mum cat of the year had poor nutrition whilst pregnant, and I saw the effect on her babies, it wasn't a pleasant thing, and not one I want to have to go through again, or put a mum cat through again.