Illinois Child Support Guidelines are some of the most rapacious in the nation and their notion that "child support is the right of the child" is self-serving and a load of bunk.
Welcome to the intrusion of government into your lives. Apparently, Illinois state law knows what's best for the children... moreso than the parents in question, obviously.
It's obscene that the state would take a rather sizable chunk of the lesser earnings' net income to send child support to a household making $300,000... but then, that's how the state gets their Federal matching dollars through Title IV-d.
If you did, indeed, put her through medical school, you should file for alimony (which I despise, too). But in Illinois, the state doesn't allow the parents to make decisions that they feel is best for the kids. You're simply no longer the child's main parents. The state is.