I heard this somewhere but not too sure if it was true. I loved her guest appearances on Batman.

There were plans for a spin off (at a sci-fi convention, I even saw a bootleg of the opening credits for the planned series), but it all basically changed when ratings for Batman went down and ABC wanted to make changes, including dropping Robin and making Batgirl Batman's sidekick for a 4th season. The show ended up getting canceled in any event.

I have never heard of any Batgirl spinoff ever being considered. They shot a 15-minute "pilot" film featuring Batgirl to sell ABC on the character so they could add her for the third season, but that had Adam West and Burt Ward in it and was not made to sell a Batgirl series.

If this claim of a proposed Batgirl series can be backed up, I'd like to see it.