Disclaimer: First, I am not a wise man, I often shoot from the hip when I should not, but I have a hard time turning from what I see as an unjust situation without at least commenting. Second, there is limited information available, and there are likely other factors in the mix which make this a more complex situation than it seems.
That being said, I have an opinion and everyone is entitled to it.
While you must respect your mother and deal with her in an honourable way, I don't see why you should not counsel her to apologize to your wife and to cease and desist on the comments, making it clear that her words will drive a wedge between you and her, since you have cleaved to your wife, and while you love your mother, your wife is first and foremost your family. You are now the head of that family, and caring for the emotional and spiritual welfare thereof is your #1 task.