First, find a carrier to take her in. Trying to carry her loose or on a leash is just asking for trouble. Second, ask your vet what they do for aggressive cats. My Misty gets rolled in a towel due to her effort to bite all vets in existence. They even have a sort of mask that they can put over her muzzle if necessary to prevent bites (although that does make it hard to check teeth).
Maybe look at the mouth of one of the younger kitties and compare it to your older cat's to see if she really is missing a tooth?
Honestly, you really can't get a cat like this to behave. Just remember, it's fear, not really hatred. She will be much happier if her teeth stop hurting (if that's the problem). Let the vet know ahead of time, then they will be prepared, don't surprise them. They deal with other out of control animals, they just need to know what is coming in.
If she will eat, take treats and see if you can make the experience more pleasant. (Our boys stubbornly refuse all treats while at the vet. Misty will attempt to bite all employees, then settle down in her crate to munch on treats.)
Dr. Seuss~DLH (brother's cat)~June 2007-
Misty~DSH (my cat & Mooby's mom)-?-
MooBoots(Mooby) ~ DMH(Mom's cat)~July 21, 2008-
Sunshine~ Golden retriever X white german sheperd (Dad's dog)~October 24, 2008-