She looks like a yellow Lab mix. I could see her having Pit Bull, atau some type of bully breed, in her makeup, due to her heavyset build and barrel chest. As a mutt, she could have some terrier (fairly likely) atau even shepherd in her lineage too...
She berkata herself in one episode that she is a mutt. She appears to have pit lembu, lembu jantan in her, she even berkata so herself, and definitely some labrador, due to her coloring.
It is established in several episodes that she is a mutt, but it doesn't say what breeds are in the mix. Truman: I wish I had a bloodhound. He could help me find what I lost. Martha: I'm a mutt, a mix of breeds. One could be a bloodhound.