Is the skin closed? There are two sets of sutures (at least, depends on the Dr.'s preference) involved in a spay, the first to close the abdominal wall, the second closes the muscle fascia and skin. If the skin has closed already (which is entirely possible - sutures generally come out in 7 - 10 says anyway) then you've got nothing to worry about. If it hasn't, you need to bring her back and have the incision reclosed to prevent infection and to keep her away from the abdominal wall sutures.
ETA: Can you get a pic? If the skin just look thin in that area, I wouldn't expect it to rip open... I might just keep her confined to one area. If it's actually open, I'd take her back. They might tell you it's just fine, but it's not worth risking an infection at that level.
Do you have a gaping skin wound or does it look knitted together?
Skin heals at about 7 days post op but is not fully healed and strong till 10 days post op. If it's not gaping open then try and keep her quiet until the 10 days. If you have an open wound, go to the vet's. Sometimes they can staple small wounds shut with the animal conscious, so don't worry at this stage about her needing a further GA.
It might be an idea to get a wound protector collar for her to stop her licking at it and making it worse. You could pick this up at the vet, might also be a plan to let them know she's decided to remove her stitches early!
After 4 or 5 days her incision should be healed sufficiently to be ok. Keep a close eye on the incision and call the vet if you see anything worrisome.