I think the dog died too. Maybe i'm biased but as a dog owner, there is nothing on this planet that would make me give up my dog if i didn't need too. And despite all of Tanya's weird behaviour now, there was a time she was a bit more stable and it was clear she loved that dog a lot. I mean she even named a product in her failed beauty line after her. Looking at her life, there doesn't seem to be a valid reason as to why she would give up the dog. She's always at home, has help around the house, and Martha is tiny, she's not going to need the same kind of attention as a Doberman or German Shepard.
I guess you may call me naive but I genuinely think if she was struggling with the dog she would give it to Jim, she's a lot of things but I think she cared about Martha enough not to give her away, but to give her to someone she knew and loved. Which leads me to believe that Martha died somehow and it was entirely Tanya's fault. The fact that its not been addressed at all, suggests there is A LOT of guilt surrounding the issue, and it could cause a lot of commotion if the truth did come out. Sarah's little dig too suggested whatever happened wasn't good. I'm not talking about her getting hit by a car, or anything like that, as mistakes do happen and if she spun the story right i'm sure she'd get a lot of sympathy. I'm thinking negligence on Tanya's part that would potentially ruin her career. I don't think we're ever going to find out what happened to little Martha, but I hope whatever happened to her, she's happy and safe, maybe with a new family, or most likely in doggy heaven.