
Unfortunately as many of my girls went into secondary inertia, we've probably had more C.Sections than natural births, in fact we have!! In every case I live in hope, but in most cases the moment they felt pain, it was ouch mum, give up. That's bassets for you. But even knowing this might happen, I always gave them the benefit of the doubt and let them start the process, even if after a little while, we ended up with the vet for a Section rather than leave them to just sit there. I've never had a problem with bonding. In fact the 'joy' of a C.Section is the bitch is usually still pretty zonked out when they first come home so you can get the puppies latched on and nursing, getting the first milk, before mum is really aware. If there's any resistence, then you just lay them down, and latch a couple of puppies on, reassuring them that it's fine. Nature usually kicks in and off you go.
In your case, and I'm more inclined to think things will be much different once dilation starts, and she's bound to be 'tight' when examined internally by a vet??, I'd let her start and if you don't see her progressing, get her in for surgery. If she had 3 matings, that would surely have opened her up some? I'd call the vets ahead to warn them she's started, so they can organise their schedule to include your possibly need for a C Section. Trouble is Sods Law this will all kick off during the small hours, so make sure you have a contact number to hand, just in case. Whatever you do, do not let her go on struggling, having strong contractions for much over 1 hour, each delivery, without seeing a puppy born. There's no point letting her become exhausted, risking her life and those of any unborn puppies when realistically these days, a C.Section is quick - she will have extra recovery to get through of course, so if she can deliver these naturally, so much the better.
I'd not let her go over by more than 2 days from the first mating, even if conception didn't take place right then.
Good luck - and I'm sorry for your confusion...... I'd tend to listen to experienced breeders to be honest. Vets know the theory, or should, but not always the practise!!!