Have you inserted your finger gently into her vent? I have had this happen with mine when they first started laying. Each time I had to "feel around" inside the vent until I located the soft shell, then gently work it out to where I could get ahold of it. Then I would gently tug - the hens begin pushing, so I tug with each push until I get it out.
I did this while soaking them in warm water. I have done it numerous times, and it always worked. I hope you will have the same luck. I've only found soft shells, so I don't know what to tell you if it's a broken hard shell. But I do suggest if the warm soak does not work, gently insert your finger and see if you can find anything.
Best of luck,
Penny