I was also a bit confused when she just jumped on the unsub. I mean, they have dealt with unsubs like this before, and this is the first time a character has to go in a fight to get the weapon out of the killers hands. It would have been fun if he attacked her (and it would have made more sens too).
But I'm still happy she got to kick ass, it's the first time we see her take down an unsub like that.