Welcome to BYC. Sorry this is what brought you here.
This should be in the Emergencies section for faster attention. Not an expert, but if you provide more info it's helpful. Age of hen, last time she laid, how are her poops. Pics of the vent and poop will be helpful.
In the meantime you should separate the hen for her safety. Good luck!
Hello and welcome to BYC. You found an Amazing Poultry Community to be a part of, with many knowledgeable members who are willing to help you along your journey with any questions you may have. Enjoy