So, can someone tell me what's up with Zoe?

I've gotten the good, bad and special endings, working on neutral now; but I feel like we learn almost nothing about Zoe. Why is she blown about like a leaf? Not that it's a bad thing, it's pretty rare to have such a character these days actually, but I expected (or missed!) an explanation.

Regarding Simon; was she coerced? Paid off? Blackmailed? Did she not even know about Richard's meddling and just happen to treat Simon? Did she find out? Does her guilt stem from this (and doing nothing about it), or is her guilt that of being an overworked healthcare worker who couldn't help everyone in the disaster?

Also, it seems Dr. Glenn's hostility might just be a way of mentally putting herself down; but there isn't an equivalent element for Simon or Richard? Or they're just less clear to me for whatever reason. I feel like I've missed something important here.