I'm sorry if this has already been brought up, but Lisa, have you considered trying to carefully reach into your banty's vent with a lubed finger and help work the egg out? I worry about anything breaking in there, but at this point, what else can be done?
This thread may help a little (post #2):
https://www.backyardchickens.com/t/431740/eggbound-hen-help-please
This thread has a different suggestion on post #9
https://www.backyardchickens.com/t/334867/eggbound
This thread may help a little (post #2):
https://www.backyardchickens.com/t/431740/eggbound-hen-help-please
This thread has a different suggestion on post #9
https://www.backyardchickens.com/t/334867/eggbound