And wildly OOC. She's been the only person throwing shade at Elena for even considering Damon as a romantic option. And bless her for that. Damon may be a little more reigned in at the current point, but he's had 150 years of flying off the handle and murdering tons of people for no reason. So for Caroline to suddenly start swooning & dropping panties over a guy who is like one hundred times worse than Damon...?
If she were to do the swooning & panty-dropping, then I'd agree that's OOC. Obviously that hasn't happened yet. I would still say that Caroline hasn't been at her best when dealing with Klaus...but still 100% in-character thus far. I still believe that line she worked into the conversation while waltzing with Klaus might be the funniest/saddest combination for Caroline ever. "...I happen to be Miss Mystic Falls." It's funny because in a small crap town full of fellow townies, you know that no one wants to talk about her pageant win anymore. Old news. But this new guy who seems interested in her doesn't know about her only claim to fame, so it's important to her that he knows who holds the current crown. She isn't that far from the girl in the Pilot who lamented the fact that, despite her best efforts, "I'm never the one." And she clearly likes the attention from this guy everyone in her social circle has been talking about forever. She is currently under the dangerous assumption that she has some power over a very powerful man. She thinks she can talk to Klaus anyway she wants and he won't hurt her. Just a crazy illusion in her head. I hope she snaps out of it soon, but I think the writers have done a good job with this from Caro's end. I just believe they understand this character better than any other on the show.
And I certainly think she felt some serious guilt after the ball. You could hear it in her short message to Tyler. She was already disappointed in herself. It's strange to me how differently Caroline behaves around Matt, Tyler, and now Klaus. Matt brings out all of her insecurities - she often seemed weak and clingy. Around Klaus she is all defiant and feels oddly in-control...even though she really isn't in control of anything, least of all herself. I always think she is at her most comfortable around Tyler. She doesn't have a need to impress him in any way. And he seems comfortable with her in control, as he's been around strong females his whole life. TYler brings out the best version of Caroline. But even when interacting with Matt in S1-2 and Klaus now, that's still negative aspects of Caroline's personality coming out that are very real. But with Tyler, the messy parts of her personality get relegated to the back-burner. You don't see them nearly so often because she doesn't feel a need to try so hard.
I'm assuming his actions were completely of his own volition at that point because he was pretty much doing the exact opposite of anything Klaus would ask him to do, ie. getting Matt to take Caroline home (after Klaus had already threatened her life) and actively trying to get as many people off his property as possible. So, yes, I think him drugging was actually Tyler making the choice for Caroline as opposed to letting her make it herself.
I've always thought that was Tyler overcompensating with the drugging for freezing under pressure when Caroline was in desperate need of his assistance in S2. "You didn't do anything!" has to be a line he flinches to in his nightmares...if we are to believe Tyler cares about Caroline at all. Instead of not doing anything at all, this time he did way too much to "help" Caroline. No matter whether your heart is in the right place or not, you cannot take free will away from a self-admitted control freak. Not even for a single night. So maybe we can assume that Tyler sometimes chokes under pressure. His decision-making isn't great when it most needs to be. Definitely a problem he needs to overcome at some point.