I'm sorry you are having such a hard time. It must be hard but it does seem rehoming might be best for Zena.
My neighbour recently took in a dog that needed a home. The dog's owner, poor woman, suddenly inherited the dog when her Dad (human Dad) died and tried her best but just could not cope. She put the word out to everyone she could, including her Vet, the dog's previous Vet, and the boarding kennel she was using a lot at this unsettled stage in her life. My neighbour had used the same boarding kennel for his previous dog and the boarding kennel owner put the two together.
It was a match made in heaven. Lucy is a lucky dog, so is my neighbour and so is my dog as they have great plays together.
Sorry for the long story but this can have a good ending and I hope it works out for you and Zena. Contact everyone you know personally first, is my suggestion. Including any professional who has had contact with Zena, like your Vet, a training centre, a doggy day care, a boarding kennel. People who know and like you and your dog are the most likely to offer help that is in the dog's best interest. Good, good luck.