Coturnix that lays rotten eggs!

I have an English White Coturnix that lays rotten eggs. She has ever since I bought her about 8-10 weeks ago. I don't know how old she is but I know she was at least 4-5 months old when I bought her, who knows she may be up to a year old.

These eggs are very thin shelled, black or rotten green in colour, and are just all around disgusting. She acts fine, eats normally and its a high protein diet, has free access to fine oyster shell. She doesn't act sick and doesn't have any lice or mites (I dusted them about a month after I got them).

She doesn't lay regularly. Maybe an egg a week and they are all like that. I thought she may have been eggbound or something but she doesn't act sick and her belly seems normal. She had started to lay a bit more regularly and the eggs seemed to be improving but now I'm back to square one.

Does anyone have any ideas on what is causing this? Should I seperate her and give her some antibiotics just in case? Or should I just be done with her and use her for puppy training?

That's why I'm concerned.

I'm not sure if its ACTUALLY rotten or if their is some problem with her ovaduct or if its an infection etc. The outside of the egg is slimy and the yolk and "white" of the egg are both greyish green or black in colour. The only thing that it doesn't do that you would expect of a rotten egg is that it doesn't stink. The next time she lays one I'll take a photo, never thought of that.

When I say the eggs are black, I mean, BLACK! Its not a normal egg. If the egg was just thoroughly put through the "paint shop" then I wouldn't worry but with the fact that the egg shell is usually non-existent and the inside of the egg is WAY past normal, I just don't know what is going on. I am not a squeamish type person, put I don't even want to touch these things when she lays them.

If she was acting sick then at least I would have an idea of how to start but she is acting normal, walking around, eating. She is a very calm English White and I have read that the pure white Coturnix can have a higher mortality rate and she is a pure white hen. No spots of colour on her anywhere.

I'll go check the pens and see if she will be a sweety and actually lay an egg so I can take a photo.

I can't get gamebird feed here but they are on a 25% protein crumble. Its a mill blend. All of my birds are on this and I haven't changed the feed at all. I currently have 11 breeders and another 20 young birds (not egg laying yet) on this same food. She is the only one that has this condition.

Since she only lays very sporadically I have no idea when she will lay again but as soon as she does I'll update this thread with a photo.

I appreciate you looking into it for me.