I think Bailey would love to have a buddy, since it sorta sounds like Peeg doesn't really want much to do with her anyway, she would probably like someone to play with I would definitley go for a Rottie, they're awesome dogs Plus, you've liked them longer than you've liked Shih-tzus. I'd go with a female Rott though, just because they aren't as rambunctious as males and they're probably alot closer to Bailey's size. I've also found that with the females, they are usually easier to train and just seem to bond better with their family. I'm not saying that the males don't but from my experience with Rotts that's just what I've found. Good luck with your decision!