Mine was a male that continued spawning. He led a great life right up until the very end when he started losing weight. I think other complications set in due to stress of trying to correct himself. He lasted 3 years head standing before I had no choice but to euthanized him.
I don't see the traditional swelling in the mid-section so I still feel this is the result of hitting the tank. Have you noticed if she's losing weight?
Personally, without the bulge in the swim bladder area, I would keep her around, but I'm a softie when it comes to euthanizing. If she starts looking emancipated, that's a different story.
Have you tried some epsom salts?
When I was five years old, my and my grandmother were rear ended in a bad accident. She injured her neck and was in terrible pain and wore a neck brace nearly the rest of her life. When I was 36 and she was in her 80's, we went to a nursery looking for some shrubs for her house. She tripped and fell over a railroad tie and everyone freaked out and ran to her aid. She got up, took off her neck brace and never wore it again. Maybe your discus will hit the tank again and be fine? Lol...