I had this same thing happen to one of the people that bought one of my pups this summer. I was willing to take the pup back, but she was so upset and didn't want to have to bring the pup back. I told her to give it 3 weeks and see. Sure enough - the older dog and my pup are best of friends now.
When they were having problems in the beginning, my pup would snap and bark at her older (golden retreiver) dog and she was afraid that mine would bite hers. I said first of all - my pup is so tiny (he will probably be only 4 pounds fully grown) he is probably so afraid of this hugh dog next to him he doesn't know what to do. And if he ever, but I was sure he wouldn't, bite my pup couldn't do too much biting to the older dog. So she tried it a few more weeks and now she says they even sleep together and are the best of buds.
My pup does steal the other's dog bone though. Well, yorkies do usually rule the house! No matter how big they are!
So you might want to try it a few more weeks. When you bring a new baby into a home it takes awhile for everyone to adjust.
T.