The reason that I mention this is that unlike Phil, Elly cannot and will not see that Michael is allowed to play the trumpet just as a useful skill. If he plays the trumpet for fun instead of making a career of it right the Hell now, he shouldn't bother because he's not being serious. This constant badgering about how wanting to hang out with his friends instead of being berated by a lunatic getting ahead of herself is going to wreck his whole life so he'd better plug away OR ELSE is pretty much guaranteed to make him want to quit. Not, of course, that Manic Mommy sees her "excellence NOW!!!!!!!!! or die a failure" ethos is why Mike felt like his trumpet was a torture device; she never sees her horrible parenting as being horrible.
Then again, we are dealing with a mercenary jerkwad who never does anything without the expectation of money coming her way. Most of why she thinks Mrs Walsh is a tight-wad is that she can't admit that she was expected to volunteer her time and money and most of why she worked at the library was to get paid. Doing things without getting cash in return is so alien to her way of thinking, the idea of Mike doing anything without getting anything back is as baffling and wrong as the idea that she doesn't deserve to be paid back in full for parenting him.