I would get the other dog. At first the 2 might not seem to get along. They should in time. It is rare for dogs to not adjust to another dog, although it can happen.
I had a 9 year old Yorkie and brought in 2 puppies and at first my dog stayed on the back of the couch and I thought I had made a huge mistake. However, he started to play with them after a few weeks, once they stopped jumping all over him every time his feet hit the floor and now they are all the best of friends and he will jump in and wrestle with them.
If the dog remains aloof then enjoy your Yorkie while she stays aloof, but this might bring her out of her shell and let your entire family enjoy her.
My older Yorkie is all mine but the puppies love everyone in the house.
I would get the other dog if you are considering it. Remember that it may takes several week and possibly even months for the two dogs to really get along. Our English Setter got along with my older Yorkie within a week of me bringing home a 9 year old, but it took him 2 months to adjust to the puppies.
Good luck! We would love to hear how it goes if you bring home this Yorkie!
__________________  It's raining Yorkies here! LOL Teek  ,Rowan  , Raksha (Grand Puppy)  , Raelyn |