You must take her to the Vet ASAP.
You need to go see your vet if there is a wound and it smell then it might be infected a bad smell from wound is not a good thing, i would wash it with warm water and look for a visible wound if not then it could be a mammary tumor feel the mammary if you fell a pea size bump or bigger that is hard and does not move it can be tumor some are benign some are malignant usually if the bleed it isthe that bad one, so pls take her to the vet it can be a simple would or something much worse only a vet can tell you for sure. Even if she is spayed she still can get mammary tumors it is only very preventive when spayed before there first heat the more heats they have the greater their chances are of get this. And did the hard time walking start when the teat problem started or before it could be her age and arthritis for older age dogs or hip dysplasia in larger breed is is common but a vet can help more, see one soon. Let us know how she doing and hope it not anything bad, thought are with you, hope she better soon.