Mostly, I think the writers/producers of SGA are fucking boys' club and I don't trust them.
However, I like Keller as the woman who's desperately trying to fit in and lies to fit the situation. Or plays what she thinks she wants the people around want her to. (I know people like this rl and they drive me batshit.)
To Weir, Keller is the nervous new employee. She's the kid taking Carson's reins and hoping to live up her boss' expectations. She's on the first day of a new job.
To Sheppard, Keller's the adult doctor who makes the decision to let Rodney activate the Nanites. She tows the hardline. Sheppard is not quite an adult with his leadership experience and she is an adult in her doctor role. (Note: I am talking about Sheppard's lack of administrator and big decision everyone's fate on his shoulders traits; he does great with military protocol and dangerous missions but he's no Elizabeth or General Hammond. Sheppard would rather sacrifice his own death than risk others.)
To Teyla, Keller's against the nervous doctor who's frightened of off-world mission, especially danger. Teyla is the action hero; she's the leader and she's kicking ass. Keller isn't even the sidekick. She's the bystander who got caught in the middle and the damsel-in-distress. And maybe for Teyla to collect her cool with her missing people, Teyla needs the damsel-in-distress, who's terrified of danger, to keep her focus on getting them out alive and not on a suicide mission to destroy the people whom she believes are responsible for the downfall of her people. Keller tells Teyla about her family as family is what matters to Teyla at that moment.
To Ronon, he's already thinking of the woman he was with on his planet. He's made the connection and spoon feeds it to her, and then she strikes gold with having to do something about what's going on. Keller plays a little more innocent, a little more nervous in "Quarantine." People were even speculating, after this episode, if she was still a virgin. You wonder if they almost kiss because that's what you do when you're trapped and have nothing better to do. (The writers have been dipping into the crack, again.) They almost kiss when they have nothing better to do. Or is it they've made a true connection...
With Carter and McKay in "Trio," Keller's the cool kid doctor with the bar tricks. She's not as frightened. Is she overcompensating as she's with the "smartest" people on the base? Is it because she feels that they're all the same level? (Especially given her guessing in "Missing" that McKay was the scared person in Teyla's story?) Carter might be the leader of the base, but she's not exactly an administer so Keller and her can braid each other's hair rope and play Who Would You Fuck?
I wonder about the thing with McKay as Keller specifically asks him if he and Katie Brown are done. And she's the one to initiate the reminder that he owes her a beer. (Where's the sexy femslash where she reminds Carter?) In her dynamic with McKay, Keller's the one with the worldly knowledge where with Ronon, she the innocent one.
I wish that I could believe that the writers were portraying Keller as someone who takes on personality traits that others want/need them to have, but believes herself to not have any personality. However, it's probably just another case of Stargate indigestion, I mean, bad writing.