Sales for Batgirls tanked pretty hard. (I've got two reasons for this, one backed by evidence, the other is just speculation)
1. The writers were Becky Cloonan and Michael Conrad. They drove Wonder Woman sales to the graveyard, and didn't do so well on Batgirls either.
(I'm sure they have their fans somewhere, but in my opinion, they are/were bar none some of the worst writers at DC I have ever read)
2. This is speculation....there is some evidence that having an original hero in a title alongside their legacy version doesn't sell well. (Partially because fans seem to favour one over the other)
Aquamen attempted to this and the series tanked badly (It was transformed into a mini if I recall correctly.)
I think this can work with GL, but I'm not holding my breath outside of that.