This tendency of hers to want to make everything that happens to her into an excuse to whine about how awful her lot is combines with an equal need to deny that anyone else is suffering. This came into play during the Mystery Disease arc. Lizzie could not be said to need attention or comfort because it was all about how bad her having a disease made Elly's existence. Why, Elly would have to pay attention to how Lizzie was feeling or waste her time listening to irrelevant chatter about some sick child and that would be just terrible. Every second squandered on the useless and unfair task of paying attention to her surroundings or anticipating disasters is a second not invested in the very useful task of decrying how no one anywhere ever has suffered as much as Elly has. This need to wander around in a fog lest she be made to LIE and say that other people are in greater need than she is seems to be why she reacts to every little thing as if it were a baffling horror that unfair cruel people actually expect her to have anticipated.
This makes a lie of Mike's belief that Elly knows everything. Elly knows nothing and doesn't want to really know what's going on. If she did, that would lead to information even scarier than the idea that there are people out there who actually like having sex: the super-scary idea that she's got to find things out instead of assuming the worst all the time.