Unfortunately I can only share my experiences or what I've read. I would observe the flock to see if the rooster pays any attention to her, some roosters will favor a few hens as far as breeding, and other will cover every hen. I have read on this site about roosters occasionally breaking necks during mating but it seems to be young roosters. So if you see him ignoring her than you could be fine, but if he's mating her it's up to you to decide if it's too much.
Some of the silkies I've owned in the past have ranged from spunky go getters, to nearly mentally disabled, so your hens personality will play into it too. Sometimes silkies act a bit odd and can be targets so watch that the rooster behaves himself. Free ranging can let you get away with more things due to the ability for birds to get away from each other.