well, it may look like an excuse but it culd also be possible that she is worried about not being around when the kids come back from school.
who do you think will take care of the kids when they are home? if it is a possibility, maybe your wife can take a part time job for now. this will ease her worries about not being around for the kids too. once they are more grown up and can take care of themselves, she can move to a full time position.
Read more