Given that she already has a college degree, the courts will probably impute income to her to either her highest wage earned or an average of what people with her degree make. Unless you accept the reduction in income. If not, then you will need to make that clear and a judge will have to decide.

They aren't going to impute an income to her that she isn't capable of earning. And while she doesn't have a master's degree, she isn't capable of earning what that degree would bring in.