First off, I STRONGLY advise against having her spayed during her season. During this time, her uterus is engorged with blood, and complications and bleeding issues are much more common, plus you will have a much larger incision due to the size of the uterus when she is in season.
second, plan to confine her from male dogs for THIRTY DAYS from the time you first saw blood. Many bitches get accidentally bred during the last days of their season. Thirty days makes SURE you are safe.
third, wait 3 to 4 weeks after her season to schedule her spay. This gives her uterus time to return to it's normal anestrus size.
Go ahead and count up on your calendar, make the appointment, and be sure to KEEP IT.
Most bitches in season don't change ALL that much. It can be a bit messy and smelly. I use unscented baby wipes to help keep her clean and fresh. A pair of men's undies tied up with a shoe string, with a sanitary napkin inside can keep spots off your rugs and furniture.
**disclaimer** Penny says DO NOT LAUGH at these photos...LOL**
Tying them up with a string like this helps keep them from slipping.
Hang in there. You'll get through it just fine.