Emergency - Female betta's back fin ripped off.

My betta, Sally, who I've had for 2 years now, used to be tankmates with another female betta. They were fine for that time, besides some aggression from the other, but it was never to the point where they were fighting. But now, the other female betta has completely ripped the back and some of Sally's side fin off. She is trying to sit at the top of the tank, and is gulping for air, and using what little strength she has to keep herself afloat. She's now being kept in sort of an emergency bowl for a moment while my mom is buying her a tank for herself, since I'm not at home. I just wanted to know what to do, and how I can help her, since she's literally my pride and joy. I'm going to keep her in a 1 gallon for now, just so we can keep an eye on her and do better water changes. I don't want her to be suffering though, and I'm wondering if it would be better for her if she was just put to sleep . I'll update with pictures once I'm sent some. Any help is greatly appreciated.

 

First off welcome to fishlore!
I would check on Sally incase that any disease could come if she is trying to reach for the surface to get air then try a betta hammock that is close to the surface so that she does not need to waste energy and can recover from the incident. Maybe someone else could give some more detail but I know that BigManAquatics is a betta guru so maybe he can help. Its best to keep Sally in another tank since in order to have multiple female bettas you are gonna have a huge tank with lots of cover with 5 or more females to distribute the aggression. Hope Sally is gonna get better!

 

She gonna need small daily water changes and probably some aquarium salt, both to prevent infection and help heal. May do wonders or may do nothing but that should be her best shot. Also nice warm 80 degree water.

 

Thank you, I'll be able to get that stuff tomorrow but I've moved her into a smaller healing tank. She's doing a little bit better.

 

Update, she's in a different tank with her own setup, she's been swimming around a lot more than before, and I'm confident that she just needs time for her fin to regrow. Thanks for all the help <3