Interesting. I don't find it very far-fetched at all that the whole thing may have started as just as "taunt," a kind of prank, if you will on Meredith. I believe I laid out one possibility in a scenario a few weeks back - where perhaps Meredith came in to tell them to quiet down a bit, or perhaps Meredith was just going to the kitchen - and Amanda, RS, and Rudy asked her to join them. To which she would have said, no, I have to study. Then they might have started something like, "oh come on, you're such a goody-girl, come on, you can study later, come on....have fun with us." Meredith could have become increasingly agitated at this. Amanda could have enjoyed this, this reaction from Meredith. This annoyed reaction. Kind of like a prank, the point is to annoy people and get a reaction out of them. Slowly, this scenario could have fleshed out more and more, until eventually it peaked in the bedroom. I don't it sounds ridiculous to some people, and that's fine - it does not sound so far-fetched to me.
The passage which you quoted - about playing pranks on her Dad - and playing pranks in general, would also fit in with the "playing victim, shifting responsibility" motif which I was discussing earlier. Because people who like to play pranks and like to generally get reactions out of people, they generally have to "explain" themselves a lot and provide an explanation for why they did what they did. In other words, people get annoyed and request an explanation from them. So they are constantly having to "get out of things" which they started. In order to not get into trouble, or to seem innocent, or to get back into the good graces of the people they did it to. Acting would play into this - I'm soooooo sorry, fake-cry, fake-cry (perhaps real cry for getting into trouble). I really didn't mean to, omigosh, I feel soooo bad now, cry, cry.
In can be not only for pranks and such things, but for generally disappointing someone. Then you over-compensate for the disappointment, by playing the victim and trying to make them feel sorry for you, to forgive you, to turn the whole situation around.
Everything above, JMO.