The thing is that it's more difficult they go to the limbo with an identity as Batgirl. Identities like Spoiler or Orphan are easily ignored by writers.
I know that Stephanie and Cassandra have been in limbo after they become Batgirl, but that only happened after many situations.
Stephanie as Spoiler has been constantly ignored (and even murdered once). In fact, Stephanie is currently Spoiler, but she is still in the limbo.