IU have the most download song by a female artist (More than 7,7KK downloads in 2015)

Heart
1,358,787

And the other songs:
Leon - 1,381,196
Twenty Three - 926,631
Friday - 876,316 (2,717,066 total downloads)
Meaning of You - 870,076 (2,440,833 total downloads)
The Shower - 680,663

We have more songs downloads, but they don't appear in Gaon early ranking

Zezé - 489,807
Knees - 462,117
Red Queen - 386,690
Glasses - 329,832

Total: 7,762,115.