I had a hen do this as well. I'd give the calcium supplement and keep a eye on her. My hen started to bleed after these types of eggs. I ended up loosing her to internal bleeding. Make sure she's not giving off a infection smell. If she is start her on antibiotics asap. Otherwise I would give the calcium and watch her carefully. My hens case is likely a extreme. Hopefully the calcium will do the trick. Keep us posted. How old is she?
They are both magnificently recovered, and it was definitely reproductive issues. Once the young hen got her double-egg out she was fine and I have not noticed any more double eggs. My older hen was on death's door by the look of it, and I was concerned she had gotten peritonitis so I did a week of tylosin. She needed it syringed into her mouth the first two days then was eating it in a mash I made, then she was ready to rejoin the flock! She is vivacious and chatty and someone is still laying yolks into the nesting boxes 