It's a good and interesting theory, but it falls apart easily because from the beginning you can see that Marianne is turned on by her boyfriend showing interest in other women, this is clearly seen in the bar when Jane sits with Peter, Marianne looks upset by the other guy and makes advances on him but then when she sees Peter with Jane she starts to get turned on, this is something that can easily be missed, I had to replay several times to realize it.
So the experiment didn't change Marianne's personality, but I like to think that it's fate that brought them together.