
First of all that's why I don't bother with all this scanning. Preferring to get a good mating, or maybe two, and wait. By 7 weeks the situation should be clearly obvious in any case. I know people say they need to know to make their own arrangements, but when we did our litters, that was the case anyway. I was lucky enough to be able to be fully committed to doing a litter.
Secondly yes, I understand you are in a difficult situation not knowing when she conceived - I'd suggest that although sperm does live for a while after mating, I'd suggest not for a week.
Personally, although the puppies continue growing if they sit beyond the 'due date', meaning a C.Section is more likely to be needed, I don't think you can do anything until she starts having contractions much as again if nothing happened with mine after 2 days beyond the due date counting from the first mating, I had mine into my vet to be examined. At which point they were usually given a shot to get things moving and if this didn't 'work', then my vet would go in - do a C.Section.
I guess you could have your bitch x-rayed to see the size of the puppies now, if nothing else?
Just to add, you do need to find a vet you can trust!!