Sometimes my colubrids will stress themselves to the point of slight bleeding from the vent when they musk. I would imagine the same could happen when a BP poos.
It's hard to give you a solid recommendation without a picture and knowing exactly how much/how bright the blood was, because it can either be nothing or it can be a sign of something serious. At the least I would recommend keeping a very close eye on her and checking to see if she's sensitive to pressure anywhere on her sides/belly.
If you think this might be a serious problem, it might be worthwhile to switch the bedding to paper towels temporarily. This will let you better monitor any discharge or minor bleeding that could easily get lost or buried in shavings.
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