Being a SAHM is really difficult, as I know from experience. You never seem to get anywhere, as soon as some job is finished it needs to be done all over again, and there are always more things to do than you can handle.
Is there any way that she can get away from it all once in a while? Is there something that she would like to try, take an art or craft class once a week, anything that gets her out of the house and away from the kids for a couple of hours a week doing something she likes? Is there a club she can join, a group that she would like to be part of?
My sanity preserver was singing in a choir, the weekly practises got me out of the house and interacting with adults, doing something I loved. Those few hours a week made such a big difference in my life. I hope that your wife can find something that means as much to her.