I have gone through your question and understand your concerns regarding your wife.
in my opinion, the history provided by you is not sufficient.
I got somany questions reeling in my mind.
1) as you thought it may be depression
. but, in depression insight (knowing about problem and worry to cure problem) will be there most of the time. but, in your case that's missing. depression will have features like feeling sad, crying spells, loss interest in daily chores, sleep disturbances, hopeless ideas soon...
2)other possibility : psychosis
. it will have no insight regarding the present problem, sitting all alone, poor social interaction, muttering or talking to self or laughing to self, fearfulness, suspecious, soon..
so, I request you to provide clearcut history for proper diagnosis and better management of her problem.