If you do not get her spayed, you will have to keep her away from ALL males for at least a month. Many years(like 100) ago I had a German Shepherd, who came into her first heat. It was over 3 weeks, and I figured she was done. She was in the back yard, and I heard a yelp! Went out, and there she was "hooked up" with a standard poodle.
He looked gay-but he wasn't! 64 days later, she had a litter of pups. When they grew up, they all looked like brindle Irish Wolfhounds, only not quite as big-but pretty big. So, it ain't over, 'til it's over. So if she is not spayed-be" vewy, vewy careful".(as Elmer Fudd would say.)
You can also get baby diapers for her, but might have to use a harness and some make shift suspenders to keep them up. But so not let her out of your sight for one second for at least a month after the heat cycle starts.
Get some female pads at Walmart, etc. and get a doggie diaper cover at petsmart/petco (the ones they have there are better than Walmart and they have velcro straps. Emma's would fall off occassionally at night though. You'll want to change the pad out right at bedtime, then in the morning and when you get home from work. Or more if needed.
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So great that you rescued too. I just love my Sally girl to pieces!!