Ending (Spoiler)
I just saw this via Netflix and think Marilyn Chambers did a very good job.
The ending shot is great. As noted by the director on the commentary, it is pretty brutal, but powerful all the same.
It is a bit confusing, though I don't mind that it isn't spoon-fed to us (see also, what happened to the baby) how she got there. We see her about to be attacked / realizing she is a carrier and then jump to her apparently dead in an alley. Well, she looked dead, as the dog was rummaging thru the trash. Note that the dog itself (unlike Santa Claus!) was not collateral damage!
She also doesn't look mauled in any way -- that is, as if the guy didn't attack her or if he did, he didn't maul her as others did to their victims. I wonder how she got there. Did she realize what she was and set herself up to be shot? Interesting little mystery. The director commentary explained why she needed blood (it isn't really made clear in the film), but didn't explain this.