Possible egg yolk peritonitis, egg bound, or vent gleet, not sure. Help please

[Bawkbok]

In addition to whatever is happening inside her reproductive system, it is very possible she is "sad over losing her friend". Chickens grieve. Extra presence by you for love and support will help her. It seems grieving I've observed in our flock takes about a week to re-adjust to an absence. It's a real thing.