I'm guessing, but she was clearly shaken up and could only use one hand. It would have been way easier to chamber a round one handed with a magazine loaded, though.Pretty sad that she does not know how to use the AR she has with her.
With hindsight being 20-20, she should have dumped the AR sooner and went back to her sidearm, which she eventually did. The combination of being shaken by being hit, communicating with dispatch and handling the suspect all at once definitely slowed her decision making process which is understandable. Dispatch should have shut up when she said she had the suspect stopped and just rolled more units.