It's gonna take a bit more TLC to get him back to full health, but there is definitely a distinguishable difference between his fins 7 days ago and today. He's also much more active. I've explained to Alex the cause of the problem and how future illness can be prevented in the future. I'm giving her my container of BettaMin flakes (my bettas won't eat it), and some links that she can read so that she takes a bit better care of him. He's looking one heck of a lot healthier than my veil tail now though..
My VT (<-----) has chomped off all of his tail and bottom fin to about 1/4 of their usual size, and is working on chomping his dorsal fin now. No idea what has sparked this behaviour as he cannot see Jayla anymore, and his tank surroundings have not changed. I swear he does it just to make me look like a horrible owner, as his fins look awful now. Thankfully, my water is clean and kept that way, so I should see new growth in a few days and no infection or rot, but he's still going to look awful for at least a couple months.