Ultra sounds wont show before 35 days (costly here about $200 with vet visit and procedure) and an xray wont usually show skelton before 42 days ($165.00 xray plus vet visit)
My Hatie on first heat had swollen breast, it's their hormonal changes becoming a woman so to speak
If you kept panties on her just like a condom you're about 99% save (joking) you should be fine!