Poorly Hen and another breaking its eggs!

If the "yellow matter " is an egg which has broken or come from a shelless egg which it has laid it could be thet it is egg bound and if it has egg in it's oviduct that can cause and infection so check her for signs of being egg bound and if it's a broken egg clean it out pronto.  Take her to a vet if you can't do this yourself.  If her lower abdomen is hot or swollen I'd get her to a vet immediately.

Egg eating often occurs when a hen lays soft or thin shelled eggs.  It can become a bad habit once they discover how tasty they are.  You can try making the nestbox as dark as possible by hanging fabric cut in ribbons across it and collecting eggs as often as possible.  If the egg shell is poor you need to look at ways to improve this.  There could be several reasons for poor shell quality such as deficency of calcium or vitamins which help absorbtion through to diseases which damage the reproductive system.  There's several threads on egg shell quality and soft eggs so search the site for advice or google. 

It could of course be just a temporary phase which will pass as well. A persistent habit which isn't related to other causes can be cured with a rollaway nestbox which prevents the hen getting to it.  However this will require some modifications to the nestboxes so check other remedies first.
All the best
HF