After playing some Cataclysm DDA, another point to consider about the guns is the noise. Using one can attract hordes from entire city towards your location, so you really need to think if it's worth the risk.
Pretty sure the "other use" for the gun that she was referring to was suicide if your bitten, and she threw it away because she doesn't want anyone to give up prematurely.
If you look at her face when she and Kurumi meet back up with Yuki at the rolling door, the right side around her eye looks burned. The eyepatch is probably to protect the burn while it heals.
Pretty sure the "other use" for the gun that she was referring to was suicide if your bitten, and she threw it away because she doesn't want anyone to give up prematurely.