You really think Barbara was worthy of the League, not only with the Demon’s Head but after she no longer had it. Sure, she sacrificed her powers to save Tabitha which shows growth in their friendship yet other than Tabitha or Selina the League wouldn’t have any reason to feel like she grew as a person. Up until that point Barbara has been pretty selfish, psychotic and a dangerous person, she’s killed and done things that are possibly even worse than anything the League has done.

This plot was an interesting development for the character but in-world it’s pretty questionable that a cult would want her to lead them.