My mom lives about 1,000 miles away from me, too. I just spent 4 days alone with her on a mini-vacation to New York and I did not tell her. I didn't want to. I had to put up with her asking me if I wanted to go to the hotel bar for a drink every blessed day... but I just said, "Nah, not really" and let it slide. I almost had to get up and leave the table once at dinner when she ordered a really strong martini and the smell of the vodka hit me, but I sipped my iced tea and took a few deep breaths and walked out sober.
If you're not ready to tell your mom, don't tell her. I don't know if I'll EVER tell my mom, and I'm ok with that.