That, I am not ashamed to say, is sheer idiocy.
You’ve convinced them to not even try.
You’ve driven the notion of self-defense from their minds.
You’ve made them victims because the one option provided is far beyond their capacity, and they’re smart enough to see at least that.
Assuming she does buy such a .50AE cannon, assuming she can pick the #@%^ thing up, assuming she can get her hands around the massive grip and pull the heavy trigger, she now has a gushing gaping gash on her face where the thing leaped from her grip and smashed her forehead, she can’t hear a #@%^ thing because the blast is deafening indoors without serious hearing protection, and now horrible things are being done to her because she missed ‘cuz she couldn’t aim that massive thing because it’s too heavy, too powerful, and she never practiced with it for those reasons - and now her assailant knows she is unarmed, defenseless, debilitated, and has REALLY P!$$#ED HIM OFF.
Just because you think a quarter-inch difference in diameter is so much scarier than a pathetic little .25 caliber.