
Yes, she can be swelling for a couple of weeks before she starts bleeding. From now on, first thing every morning press a clean white tissue on her vulva, and at the first sign of pinkness count that as Day 1. That's when you keep her isolated from all other dogs for
at least 21 days, 28 to be on the safe side. Don't leave her outside unattended, not even for a couple of minutes in your own fenced garden.
I suggest you buy a copy of The Book of the Bitch, by White and Evans (available from bookshops or Amazon) because you'll find it full of invaluable information.
:)