OK, I have to be honest...when I first read that your mom was wearing white I thought it was truly no big deal. I have to admit, I had a shower a few months ago and my stepmother wore white. Guess who got most of the wrath of the crowd that was at the shower...ME! Here's the thing, if she wears white, you will have a ton of people coming up to you going "OMG I can't believe she is wearing white" and you will have to deal with it all night long. Is it really worth the stress of the evening? Just a thought. You may want to address it now rather than have to deal with a ton of people trying to say something about it. Hope this helps.