What is the ruling on combining university studies with a part-time job, given the feeling of anxiety about not being able to reconcile between them, and the mother's opposition?

A woman may work if she fulfills its conditions. If you seek Allah's guidance (istikharah), then seek the advice of experienced individuals in your field to reach the correct decision, and then proceed with Allah's blessings. If studying while working is suitable for you, continue working. However, if work negatively affects your studies, then finish your studies first and then dedicate yourself to work. What will help you make the right decision is seeking Allah's help, supplicating to Him, and consulting those with experience.