What should a girl do who has broken two oaths, but is unable to pay the expiation in money because her mother controls her salary and repeatedly refuses to allow it? Should she fast, or wait? And what is the ruling on previous oaths for which she expiated by fasting for the same reason?

The expiation for an oath (kaffarat al-yameen) follows the sequence mentioned in Surat Al-Ma'idah, Ayah 89: feeding ten needy persons from the average of what one feeds one's own family, or clothing them, or freeing a slave. Whoever is unable to perform these three acts moves on to fasting for three days. It is not permissible to resort to fasting if one is capable of feeding, clothing, or freeing.

If someone is liable for an oath expiation but their money is absent, they must borrow if they find someone to lend to them; otherwise, they fast.

In your case, if the salary reaches you directly, you must deduct the value of the expiation before handing the salary over to your mother. Any expiations for which you previously fasted, you must re-render them by feeding or clothing, and that fasting will be considered a supererogatory act. However, if the salary reaches your mother and you are unable to provide the expiation's value or borrow, then fasting suffices for you, as you are legally considered to be without the means.