My mother remembers on motzei shabbos that she made the berocha for hadlokas neiros on erev shabbos, but forgot to light the candles. What must she do now?
There is nothing to be done now.
If possible she should light an extra candle for the future (Rema 263:1).
However, if her not lighting was not fault of her own (for instance, she suffers from forgetfulness or some other condition) there is no need to light an extra candle (Magen Avraham).