Why even bring it up? If your not ready to tell her and want some more time under your belt, don't even worry about it.
If your mother does notice and asks, "your not drinking anymore?" Why not just tell her your getting started early on your New Years resolutions, trying to be more healthy, lose weight, whatever and let it go.
An old timer at my AA meeting last night was talking about dealing with all the holiday parties, etc.
He said something to the effect of "We alcoholics are over sensitive about whose watching us to see if were drinking (I hope they don't notice I'm not drinking) or not drinking. Normal drinkers won't even notice if we're holding a coffee or a glass of wine and those that do point out that we're not drinking and goad us on (come on join the party) probably have a problem themselves."
Not sure exactly what he meant but it sort of made sense to me.
I don't know, I'm rambling, but I wouldn't worry about what if scenarios days from now. Stay in the now and stay sober.