i’ve lived with my unstable mom diagnosed with bipolar syndrome for all my life. best thing to do is to take swift action before you get your hands dirty. ditch the air gun and any other weapons for self defense. if your really concerned she is going to hurt you, move to a safe place. a jury isn’t going to think of you as a rational or responsible juvenile if you respond to your mom with violence.
if you really want something for self defense, carry mace. from my experience pepperspray is economical, effective, safe (in the long term), and most importantly legally viable (considered a misdemeanor).