Juno throws pickaxe, follows it up with neck snappage, not even a second of hesitation.
Juno pulls out a pickaxe that had gone straight through her kneecap, while standing, and raises it in preparation to fight the six or so crawlers coming at her.
Sarah kills a crawler. With her thumbs.
Also, the moment when the so-far panicky and terrified Sarah totally snaps and wipes out an entire family of crawlers, one right after the other, using nothing but animal bones. She's scary, but awesome.
On a similar note, Sam, who had so far been the comparatively wimpy cutie pie protected by her older sister, managed to climb onto a crawler's back upside down in midair and stick a knife in it, all with her throat slashed open and about three seconds left before she bled to death.
How about Becca's single handedly climbing across that cavern and hooking the equipment up with one hand? The actress went through a ton of exercise for that stunt.
The moment in the first film when Juno is sneaking through the cave when she spots a Crawler in the distance. She raises her pickaxe with a look of absolute terror on her face, ready to defend herself, but the Crawler doesn't spot her and moves away. Juno's facial expression then changes from "terrified" to "highly pissed off and ready to kick some ass".
What does the aging out-of-shape manly sheriff in the sequel do when confronted with a crawler screaming in his face for the first time? Punch the little shit in the face!
Juno managed to Survive the last two days on her own with a completely destroyed knee cap, and some how survived the entire army of crawlers attacking her at the end of the first movie.
Greg killing a Crawler with a power drill, after having his throat torn out. He then pulls a Heroic Sacrifice to save Cath, which is only slightly mitigated by her dying only moments later.