T.M.
I was the mother of an exceptional 2 yo as well. At 5 months she spoke, by one she was speaking in complete 5+ word sentences. I never found any particular playgroups that would facilitate her abilities both socially, and academically, because most children her age were not on the level that she was. Now she is an almost 8 year old, who is moving into 4th grade and reading on a 6th grade level (she should be in second BTW). What my husband and I have found is that it really is easier to let her lead the way as far as her abilities go. She showed a gifting in music very early also, and we have her in piano/clarinet lessons. We also opted to take her home and homeschool her. This works amazingly now that she is older, because she can work academically where she is at, without it suffering her ability to make friends in her own age group doing activities such as brownies and gymnastics.
For a 2 yo, your best bet is to continue to allow her the access to other infants (the ones in your home are fine, because she is learning the social skills), and allowing opportunities for her to grow academically on her own. Separating the two (social and academics) is what really has helped our daughter. You will also find, that as she gets older, she will seek out friends that are more on her wavelength. Our daughters friends are all between the ages of 10 and 13, or the friends that she has in her age group 7/8 are all also very bright.
Good luck.