What gender are her cochins? Are those all the birds she has? if they're hens and your cockerels are full size, that doesn't sound like a good mix to me.
Anyway, if the cockerels are full size, at this age they're probably about the same size, so it would be a good time for introduction. Just be sure there's lots of space and hiding places. And once is best. Moving them back and forth would be more stressful than just letting them take care of it. Let them work it out, don't keep pulling birds out unless there's blood involved.