The most successful is the Spice Girls, 85 million sales.
destiny's Child had sales of 65 million.
https://en.wikipedia.org/wiki/List_of_best-selling_girl_groups
I have no idea who 3LW were.
Wiki says the Andrew Sisters from the 1940s was actually the most successful with sales of about 90 million units or perhaps the Supremes from the 1960s too.
extract.
Accurate total sales of the Supremes records are unknown – estimates range from 20 million records up to 100 million records.
The group Andrew Sisters is not on the listed because none of their records were certified by organisations that represent the music industry, although their estimate sales are 90 million copies worldwide
And the most successful song of all-time by a girl group is The Ketchup Song by Las Ketchup. 7 million sales.
https://www.youtube.com/watch?v=AMT698ArSfQ
the most successful album by a girl group is Spice by The spice Girls.
https://en.wikipedia.org/wiki/Spice_(album)