Blood on her fur?

Last night I went into the bathroom and Peanut always follows me so she can get a drink out of the faucet. While she was drinking I noticed a dark spot on her back end. It wasn't near any of her "openings" if you will, it was on the edge of the fur, towards the side in between the two openings and it was a perfectly round drop of blood. I would say it's about 1/8" in diameter and very dark. I took it off with some toilet paper and noticed a little bit of what appeared to be mucus (sp?) in it. Sorry to be gross.
Now -
1) It obviously wasn't there 30 minute prior cause she was all over my daughter and I and my bed and it would have wound up on one of us or the bed.
2) It wasn't near any of her "openings" as I said and I examined them to make sure all looked ok (gross I know, but I had to) and there is absolutely nothing wrong back there that I can see.
3) I didn't find anything in the litter boxes
4) From what I've seen, none of the other cats have "injuries" or anything and I haven't heard any fights to warrant any injuries.
5) she's acting 100% fine. Absolutely no change in her demeanor, size, shape, nothing
6) They are all indoor, so I'm ruling out "critters" from the outdoors. Especially since it's winter here and cold.

Any ideas? Should I be concerned about this? I actually was freaking out most of last night because it was just odd and now I'm terribly worried about her. Should I make a trip to the vet for a drop of blood? It just seems dumb, but maybe there's something wrong. Maybe it's not even from her.
And now here's the really stupid question. Even though she's spayed, since it was so close to her backend, can cats still randomly have a little blood here and there around that "time of the month"?
I'm just worried about my little girl (and the others if it came off one of them). What should I do?

If it were me I'd probably watch her (and the rest of the cats) very closely for a day or two. I dont think I'd run to the vet for a drop of blood unless the cat were exhibiting other symptoms.

I would watch her carefully, especially when she uses the litterbox. A spayed cat wouldn't have any "monthly cycles" as their uterus is removed. It sounds like this could be stool-related, but any time I hear about blood on that area, I worry about urinary blockages. Make sure she is still using the litterbox normally--if she looks like she is straining, she needs to see a vet.

Ok, I've "inspected" Peanut twice today - absolutely nothing! She's 100% clean. I've inspected all her sleeping spots for any sign of blood - nothing. I've also inspected all the litter boxes for any signs of blood there and nothing that I could see.
It's very difficult for me to watch her use the box because I have all of my litter boxes in a small room in the cellar. It's the Kitty Potty (formerly my shop - I don't build much ) The door remains closed and I have cut a hole in the wall for them to access the room. Thing is, Peanut is my only baby that doesn't sleep upstairs during the day. She has a sleeping spot in the cellar and sleeps there most all of the day. So in order for me to see when she's using the box, I'd have to hang out for the day in the cellar.
I'm sorry this seems like a trivial thing and I know there are many others out there with bigger problems and bigger worries with their babies. I guess I"m just a nervous meowmy (actually in this case a nervous Grandmeowmy. My 12 year old is her official mom).
Not sure what to do from here. Maybe it was nothing at all. It's just strange is all. Blood out of nowhere. For now I'll keep inspecting the boxes, watching her demeanor, and I've put a white blanket in her sleeping spot so I should be able to see anything.

It's not trivial, you're taking good care of them, that's what it says to me

Trivial NO ... Just keep a eye on her

Definitely not a trivial thing. Can you have your 12 year old camp out some afternoon down there (maybe with a book) to see if she can catch her in the act? My main concern would be if there is any sign of distress while using the litterbox. Or, it could be a one-time thing.

Originally Posted by cloud_shade

Definitely not a trivial thing. Can you have your 12 year old camp out some afternoon down there (maybe with a book) to see if she can catch her in the act? My main concern would be if there is any sign of distress while using the litterbox. Or, it could be a one-time thing.

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Actually I was considering moving a litter box to a room and locking Peanut in the room. That would force her to use the one there. Hopefully it won't be for too long. Just long enough for her to use it.