Thanks everyone for the replies. I've been up since 4am with her. I took her outside, and she started vomiting. Actually it scared me a bit because afterwards, she laid down in the grass and refused to move.
I took her in this morning, and we are assuming at this point that the blood was from her throwing up. Tests have been run, but I won't know anything until tomorrow. She had X-rays, blood work, and a urine analysis. We couldn't get a poop sample.
Since my poor baby panics being left with strangers, they let me take her home. We've got medication to coat the stomach in case it is ulcers, medication to prevent vomiting, and some special canned food (which she's had before and likes, but now refuses to eat it).
Btw, she is spayed, and doesn't chew on anything really.
I'll post an update when I know more.