Is it permissible for a university student to withdraw from studies that involve mixing of sexes, despite her parents' objection, and would that be considered disobedience?

We ask Allah to grant you steadfastness, for a person's preservation of their religion is a great objective. If you can complete your studies in a way that avoids temptations and mixing, such as studying from home and using private transportation, then do so, especially since what remains for you is little. This would bring joy to your parents and avoid an awkward situation if the marriage does not happen. However, if completing your studies will lead you into temptations that you cannot avoid and will corrupt your religion, then you must abandon them. You can use indirect speech (ma'arid) or even lie when necessary to answer people and your parents about why you left your studies.