burning her candle at both ends

Burning her candle at both ends, or burning a candle at both ends, means to work very hard on something and stay up late at night working on it. The phrase refers to one end of the candle being lit for work done in the daylight, and the other end of the candle for work done at night. If someone (she in this instance) works late at night, they have more than likely worked during the day and the night.