What should a girl do who suffers from memory loss and cannot recall the number of past fasting days obligatory upon her, and how can she atone for that?

If a girl suffers from poor memory and doubts the number of days of Ramadan (definition) fasting she still owes, she must fast the days she most likely believes are still due to absolve herself.

As for delaying the making up of Ramadan until the next Ramadan arrives without a valid excuse, she is required to pay expiation (kaffara) by feeding a poor person (one mudd of food) for each day she did not fast. This expiation is not repeated if the delay extends to a third or fourth Ramadan.