Hi Keli! I don't blame you for being confused, there were some parts that I drew confusedly, and other parts that I meant to be obscure.
I'm not sure what "big thing" you mean, but she came back to the surface because the lasers forced her back--that was what I didn't show very well on page 93, in fact, which is supposed to show her floating back up the entry hatchway, because the lasers have now filled up the rest of the interior.
The Major meant to fire in time, but he didn't count on the robot thing spotting him and firing so quickly--in other words, it was just a lot faster than him. And I think Selenis was somewhat skeptical that his gun would have much effect on it even if he *had* got a shot off.
As to why it proceeded to act funny after that, I'll just have to leave that to your imagination--or you can keep reading and see if future events offer any clues. : D
Selenis was there hunting for Perriman technology, and she saw an unexpected demonstration of it, but didn't manage to retrieve anything herself, so I'd have to say no, she didn't really get what she was after--again. : o