I know my life with my MIL was always so difficult all through my married life, I actually allowed her to ruin my Chirstmas for many years just to avoid not hurting her feelings, and not wanting to 'Set' her off.
I'm assuming you love your mom and have a normal relationship with her, that's what I got out of your post so I hope I'm right
As you know, Your mom is causing the problem. Since you love her it's It's probably really hard to let her know that she's that you think that about her.
The problem will only get worse though if she doesn't stop now. One day your wife will resent her because you will always have to bend for her, and than you will be caught in between both woman you love. My husband is there now.!! lol Not a pretty sight!! lol
I think the real problem is that your mother feels a little threatened by your wife. You can never say that to her though.
I don't think you should really tell your mom you want her to butt out because that will only cause hard feelings, she will think you don't love her as much as you love your wife (yep she will). I've been married for 30 years and my MIL still gets between my husband and I (constantly makes him choose) even thought I tell her to stop My husband can't seem to put his foot down and keep it down. So she knows he will 'side' with her.
The only way you mom will back off is if YOU tell her too. She won't do it if your dad tells her, or if your wife tells her, truly only if you tell her.
But you have to do it in a delicate way, not like you would tell anyone else to back off.
If you can do this now in your married life, and do it so NO one gets hurt feelings I promise your life will be so much easier later on. I wish I insisted my husband nip it in the butt immediately.
Maybe if you take her out alone on a lunch date, and tell her that you sense she might be feeling worried that you don't love her as much any more since you have a wife, it might work because mom's really don't want to hurt their boys.
Tell her that you will always love her and she will always have a special place in your heart, blah blah blah lay it on thick with mom. Than bring in the part where you (not wife) just wanted to start a something a little different, a new Christmas tradition that everyone could enjoy, since your daughter loves everyone you thought it would be nice for <I>her</I> to do it this way. Something like that . Try to keep your wife out of it, don't make it her idea because mom might feel it's a competition.
It's a tough one but try to fix it asap because I know it will get worse for you. Good luck.