Kevlar alone is not that heavy per se, standard kevlar shirt is usually weight less than 1 kg, but it wasn't that good against anything larger than dinky 22 LR and is extremely weak against knife.
Thicker vest with plastic/composite armor can be up to 2-3 kg, and is good at stopping common rounds like 9mm or 45 ACP, or maybe even smaller magnums like 357 or 44, and slightly more resistant to sharp object.
More powerful rounds including rifles requires heavy armor plate between the kevlar layer, be it metal or ceramic, and usually being 7 kg AT THE LEAST. Using knife against this one is meaningless unless it's a lucky strike.
Anyway, let's see if that wimpy-ass playah can last long with her, you know what's scarier than angry brother? scorned woman.
