Despite their cute and fluffy appearance I have always found silkies to be quite feisty little birds so I wasn't the slightest bit surprised to hear that she wasn't keen to hang out with the new flock. I absolutely love the fact that you are so tuned into her that you can read if she wants to go in with the others or not. Brilliant chicken whispering.
Starting with chicks would be good as she would be top hen but its not really the time of year for chicks and its the cold winter nights that you are concerned about. In terms of keeping her warm you could always bring her indoors to roost in a cat box if the weather turns bitterly cold but the impact that one other bird would make on the temperature of a coop would probably be minimal and would very much depend on the size of the coop.
If you are wanting company for her then two older or smaller birds might be the answer as long as they are very laid back and happy to be bossed around. If however you feel that she is content on her own even though she has the option to join the others then that may be her preference. Although we all prefer to have company for ourselves and our animals, sometimes being alone is preferable to being with those that we dont get along with.
If you dont like this idea than another option could be to get a couple of ducks. They wont speak chicken of course but will be content to poddle about with her and roost in the same accommodation......
Personally I would get a couple of silkies, sebrites, pekins, sablepoots or of course my beauliful laid back croad Langshan bantams.