Heh, so my gut was right this time around. I felt Makima would move in because for her 1) Reze is a dangerous enemy, Gun Devil's ally and has been attacking her people, and 2) she's a murderous crimimal. Although I'm not sure just how much the second point weighs for her.
And to be perfectly frank, the romance subplot nonwithstanding, Reze dying in her moment of weakness is what she deserved. SMASH that dislike button!
(EDIT) Oh and I forgot to mention how the author is really laying down Makima's personality, having her just sit next to Reze and watch with an emotionless face as she dies.