[paddys mom]

I introduced a VERY territorial 4 year old yorkie to a Chi rescue that was 6 months old at the time. I was very unsure if he would accept a newcomer so we took things pretty slow. The rescue required us to foster the chi for a week to make sure things went smooth. It went so much better than I ever could have hoped for. He was guarded at first but now they are BEST buds. I can't believe the things Paddy will let her do. (biting his ears, legs, face, when they play.) And this is a dog that for the most part does not like wrestling with dogs!

First, did you take them to neutral territory when they first met?...that helps to get them on good terms at the very beginning.
I don't know if you can walk the chi yet or if she's too young but I would recommend walking them together as soon as you can so they can bond outside.
Take all their interactions inside slowly. No forcing them to interact but let them come to each other on their own terms. The older yorkie will probably snap at the puppy but that is actually normal. If she is just yappy with him but not actually biting or hurting him I would allow the older dog to tell the younger dog the rules of how she wants to be interacted with. Supervise them with toys and food to protect against fights. Though I found that if I let paddy join in when I was clicker training the new girl and he got some treats too he thought her being around was REALLY great haha.

All in all, you have to give it time. If my brat can be inseparable with his sister any dog can come around lol!