Remember that the air temps, even if it's not that high from the floor of the tank, is always a lot cooler than the belly temp. Your snake doesn't hover 3" above the floor of their enclosure.

If there was a lot of blood, I'd be a bit worried. Did she maybe shed recently? The can sometimes be a bit rough on themselves and they can make themselves bleed a little, that's no biggy.

Another thing to consider is the possibility of it being from a feeder. Sometimes the snake can be kinda rough and it can make the feeder's belly explode (gross, I know), so maybe it's feeder blood from something like that?

Next time you have her out, take a good look at her to make sure she doesn't have any open wounds. If she does, you should make sure that she doesn't get it infected, and you might want to bring her to a vet.