There has been a lot of debate about which came first, the shot or the stabbing (even though the ME has explained the scientific evidence he used to conclude it was the stabbing). Those who disagree with him say it doesn't make sense that she would use the knife first when she she'd gone to the trouble of stealing a gun to that, I have two comments:
1). She is not a normal person...her logic and the logic of a reasonable person are two different things...maybe she wanted to kill him up close and personal so she brought a knife as her first choice and the gun as a backup option...maybe she started to worry that the gun would make too much noise.
Or
2). She did try to use the gun first but she dropped it or he saw it, struggled with her and knocked it out of her hands..it slid across the room and he scrambled for the gun, not realizing she had a knife too. In this scenario she stabs him as he's trying to get to the gun.
I know, anything's possible..just trying to offer an explanation that explains why she didn't just shoot him first.