what would make a mother keet kill another keet.as posted o my God;maria killed another keet.what would cause this and how could one keep it from happening.are there signs to look for?

Without knowing more details, e.g. ages, how long they've been together, food, living conditions, health etc. it's really difficult to say and a vet would have to carry out an examination.

It could be a form of depression that caged birds suffer from, jealousy, eating the wrong food, overdose of medication, or even disease.