Season two, she comes back and David doesn't want her around. He tries to get her kicked out several times, but she just manages to cling to him long enough to secure her position. She is completely sketchy, even BEFORE she seems like a real bad guy, with her networking, her threats against Lynne's power, her talking to Ron Wieland, and the fact that she has a TON of connections that she's not afraid to use. Just her rivalry with Lynne is amazing because of how Lynne can tell that Sherry is bad news, and rather than trying to defuse this by being under-the-radar and kind, Sherry goes with an intimidation tactic that takes some serious balls (another thing I love about Sherry is how cut-throat and open she is about everything, even though it NEVER works for her). And then it turns out that she was involved in the plot against the country, which she tries to defuse by saying she was working undercover (and she'll let you know, she did NOT sleep with Roger Stanton), and even brings in proof...but I just don't buy it. When Stanton sells her out, it's amazing because of just how much sense it makes. Only Sherry would put the country at risk just to get close to David once again.
And when she comes back towards the end of the season? I thought we'd seen the end of her, but it turns out she knew more than she let on, and she winds up getting caught by Jack and talked into spilling everything she knows. Honestly, watching a guy like Jack take on Sherry is great because let's be honest...any time Sherry is getting verbally or physically smacked down makes the audience happy. Hell, she tries to manipulate and sweet talk the little nerdy tech guy, and he winds up stabbing her in the gut. Did he NEED to stab her in the gut? Probably not. But he ran off, and Jack gave her one look as she begged for help in her wounded state before running off and not caring. Even better is after the guy dies and Jack goes back and drags Sherry with him, wounded, knowing that he needs her if he's going to recover his evidence. And just to prove she's not a one-note evil character, Sherry actually does a good thing. When Jack crashes his car in the wake of a heart attack, Sherry has the chance to escape and leave him there, but instead she comes back in order to help David, and puts her life on the line to get evidence of the conspiracy against the Middle East. This positive turn only sets the stage for Sherry's finest hour in season three.