Is it permissible to cut one's hair after the cancellation of an occasion for which an oath was taken not to cut it beforehand?

Oaths are based on the intention and purpose of the swearer. If your mother's intention was to prevent you from cutting your hair until you attended a specific occasion, and that occasion has been canceled, then there is no harm in cutting your hair, and no expiation is due from her, because the reason for the oath has ceased to exist. However, if her intention was for your hair to remain as it is for a specific period until the date of the canceled occasion, then you must wait until this period has passed before cutting it.