If your use is light, this might help your case with Mom. http://www.cmaj.ca/cgi/content/abstract/166/7/887
Also, it does NOT mess with your memory (after you're straight -while you're stoned is another story- lol) No brain damage from pot. http://marijuana.researchtoday.net/archive/3/3664.htm
Some studies suggest that it may be neuroprotectant and cause the brain to grow new brain cells. If your Mom has any illnesses, run a search on it and cannabis abstract- she might find pot is good for what ails her!
Incidentally, I'm 59, did most of my 2nd time around in college stoned to the gills, wrote most of my papers stoned (but cleaned them up straight) and graduated with honors in my mid 50s. I tutored other students and was the Bio lab tech while I went to college and held a part-time job. No amotivational syndrome here! I work as a teacher's aide (be nice to that always smiling teacher's aide in your class, it might be me!) and am a MMJ user in California. Feel free to show your Mom this post or to pm me.