I have a couple of Serama hens that grew up in my flock of silkies. They are defiantly the top of the pecking order in my flock and sassy. They are very human friendly but quite bossy with the silkies. My silkie rooster hasn't even tried to breed them, I had a young cockerel that would try and get chased around the yard by this little hen half his size, it was the funniest thing to watch I wish I had gotten a video of it. Depending of the rooster you may have trouble if he is too big for her he could hurt her. One thing I for my flock is the Seramas can fly but the silkies cant so they can always get up and away if they had too.
I see you are in Ontario, I am just south of Kingston. Seramas aren't know for tolerating the cold well. Mine did well last year as they just snuggled into the silkie pile when it was cold and we have been down in the 20s at night already and they haven't had an issue. However I've seen many people recommend they not be house in under 40 degrees. I love these little gaps and would love to get more but I’m nervous about the cold intolerance. This is one of my girls next to my silkie rooster. 
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