Sasha is wasting ammo cause she's gone crazy. She isn't killing zombies to protect Alexandria she's killing them for revenge. She went out target shooting too which is a clear waste of ammo for her but it wasn't about the practice it was about shooting those pictures and their happy memories. Also the group is spoiled now, just for a little bit, with so many supplies. Carol has chocolate. The last thing Sasha is worried about is ammo.

 

1. Yes, but they've still been kinda trigger happy since they've arrived at the ASZ (more than they need to be).
2. I assume people can hear these shots from the tower, and someone should have wondered why the hell there's so much shooting going on and said something.
3. I also assume that they keep the inventory for the ammo as well as they do with the food. They might not be as detailed as Terminus, but someone's got to realize how much ammo she's getting all the time (considering how much she's blowing through it).

 

Didn't Carol say they've got a locker full of 9-mms (or something like that) that they weren't keeping track of? If so, I doubt they're keeping that close of a watch on the ammo.

 

Yeah, it was like a plastic garbage can full of guns. No one goes in there because nobody uses those guns. The ammo would be slightly different. Most people I know keep their ammo in its boxes until they're ready to use that box (of 30, or 50, or whatever). It's not kept in a bucket or anything especially since they're going to have a wide variety of ammo that needs to be kept sorted.
I know this is all speculation, but that's just how I picture it.

Also, I think in a ZA people would be hypersensitive and observant about using anything that is limited in supply. I know I would (especially if I had someone wasteful in my group).