Was it just egg yolk or was it a soft shelled or no shelled egg (with just the membrane)? If it was soft shelled or no shelled, but intact, then she may not be getting, or absorbing enough calcium. How old is she and has she laid normally before this? What do you feed, including all treats, and do they have oystershell available for calcium? If it was just yolk then she may have had an egg break inside her. I would give her a calcium citrate +D (citracal) daily, that will help with calcium if she's deficient and it's the best absorbed type, it will also help with contractions if she still needs to expel anything. If she's a standard sized bird then 600-800 mg daily. I would continue the calcium for a couple of weeks, or until she lays a normal egg. If it was just yolk then there may still be egg matter inside which can be a breeding ground for bacteria and infection, so keep an eye on her, make sure she perks up some, if not you may need an antibiotic as well. Trying to lay a shell less or soft egg just by itself can make them feel awful, it's very hard for them to pass, and they often feel much better once it has.
If she's a new layer or a bird just coming back into lay then it could just be a glitch. If it persists even after supplementing calcium then it could be a shell gland malfunction.
