I am not familiar with the Shih Tzu but I have gone from big dogs to toy sized dog. House breaking is much more difficult. They are not clumsy like big breed puppies and their bladder is tiny. You have to watch them every minute. I assume you got an appropriate size crate for the comer. I suggest when ever you can't watch closely crate the new one. Sometimes having an older housebroken dog helps, sometimes not, you might do better bringing the new one out alone. Give him/her the idea what they are outside for. You will have to see what works with your dogs.

I have two Shih Tzus I raised from the time they were puppys. I found them very easy to house train. Never are crated and no accidents after several hours even with the 7 month old pup.The older one was raised with a boxer and they are hardy little dogs. Some people think they shud be paper trained which is rediculous as they are quite capable of going out in all kinds of weather. The biggest issue with both was nipping when teething but they outgrow that soon. I love mine and as far as small dogs go are to me the best. Treat them as dogs not like little Divas.

I also have two shih tzus and they are a wonderful breed IMO. Very energetic fun loving dogs. To help her fit in I would just suggest spending time every day with some play time - mine love to chase the ball, go for walks or play with their toys, they love to play more than any dogs I've ever owned, play play play, they can't get enough. When I got my first one I had an older dog so a number of times a day I kept her occupied with games so she wouldnt get bored. after I lost my old dog I got my second shih tzu and they keep each other very busy playing together but they still really look forward to play time and walks etc. every day as well. A busy shih tzu is a happy shih tzu lol

I grew up with one and he was a fun dog! He never had a crate and was perfectly house trained. I know they can have temperament issues but ours didn't. He had so much personality!

My mother bred Shih Tzu's when I was a child, and I remember them as being very lively, intelligent dogs. We never had any issues housetraining them; the key is consistency, and remembering that their bladders are smaller, so you have to pay closer attention.

Valuable advice, thanks a lot. I will pay very close attention to this coming new little one.