Is she a small hen? I have a great layer that is a runt and sometimes there is a little blood on an egg. I am sure the whole process of laying an egg can do some damage, esp. in a small hen or young hen. I would keep an eye on her, check her vent every day, that is what I do, you read about alot of vent prolaspes here, so it can happen. make sure you know what to do if this happens, clean the tissue gently, she needs those tissues, put prep.H, honey or sugar on the moisten tissue, alllow this to help reduce the swelling for a few minutes, then with a lubricated gloved finger gently push the tissue back in, it may pop out again, try it again. keep her in a darked area to prevent future laying until she heals up and keep her separated from the others, they will pick at the tissue and will kill her. add some oyster shells in her diet too, help to make a better shell.