I'm so sorry about Maggie. I'm going to believe that she's in someone's home being well cared for.

Sounds like your mom and you have a empty spot that needs to be filled - not a replacement, just an addition. I don't have a lot of advice about the dogs because my only dog is Disney and she is extremely laid back and good with cats. She doesn't love them but she tolerates them and I think she actually likes Jazz. They have an odd relationship.

Anyway, the shelter should be able to give you some idea on the cat's temperment with dogs. As for Elvis, he will probably be a little much for the cat so finding a easy going cat would be best.

I hope it all works out of you and I really hope Maggie returns home soon.