It's really hard to say, there is a little 'wiggle room' as you say but when dealing with any small breed that wiggle room is very small.
You say you don't want to proceed with a pregnancy which may require a c-section but you really will not know for sure until the time comes.
Vet can do an ultra sound fairly early into the pregnancy and determine how many puppies and check their development and size and you may be able to terminate the litter then if they are going to cause problems for the b*tch. If you leave it too late though this will require surgery either way.
Are Mini Shepherd AKC recognised? (sorry, I am in Australia and they aren't here)
Does the AKC have a code of ethics like we do here that does not permit members to cross breed?
Edited to add: There is a Miniature Shepherd club, their wesite is here
, unfortunately they don't appear to have a forum, but there is a list of upcoming events you might be able to attend to chat with breeders.