So if a chick is, say a week old, she would know it is not hers, even if she had only been sitting on eggs?
Silkies have a reputation for being very maternal, so she may adopt it, or she might not. At one week old, the chick may or may not bond to the hen. You could try it, but I'd definitely have a Plan B in place, wether it be returning the chick or raising it yourself.
If it were me, I'd place a chick order, give the hen x number of chicks, and then sell the rest of the chicks on Craigslist or give them to a friend or raise them myself.