she looks a bit chewed up actually.

I'm guessing you are simply feeding too large.

Two things: if you are feeding prey that are small enough the snake should be able to overwhelm them. In my experience this means that they only need to use their "neck" at first and, if the thing gives them trouble, they've got plenty of extra slack to squeeze it to the point that it can't move at all.

The basic description of constriction is that it kills prey by suffocation (aka respiratory arrest). This is only partially true. The high pressures exerted under constriction can also cause circulatory arrest as well as spinal fracture, both of which kill much faster than suffocation alone. The smaller a prey item is, the higher the chances of these other effects occuring. I have definately noticed that smaller prey items die much more quickly and are much less effective at defending themselves.

I wouldn't feed anything to your snake that doesn't give it some "slack" to work with. I've found that my snakes will use pretty much only their necks to constrict if everything goes well. However, if the prey starts to bite, they'll start cranking up the pressure and adding more coils. I witnessed this just yesterday when I fed my carpet a medium rat. He struck and coiled twice. The rat then attempted to bite him twice and he responded by squeezing much harder and coiling around the thing about 3 more times. In a period of a second or less the rat went from trying to bite to being completely immobilized.