Betta Fish: taking my family members fish.. advice please.

hello! i’ve always been super into fish keeping so i know all about nitrogen cycles and what not however it’s been a few years since i’ve gotten a betta fish. nonetheless rescue one in this bad of condition. i used to “rescue” betta fish a lot a couple years ago but it’s been a minute. so im just seeing if there’s any new tips or methods.

she’s had this fish for a couple of months. i got her a fish filter for christmas and water conditioner (yes very passive aggressive bc she refuses to listen to me). but about 3 weeks ago she cleaned the entire tank and dropped the fish in the garbage disposal (wasn’t turned on). and has gone downhill since then. they had me come over to help and i brought a almond leaf and aquarium salt but they’ve agreed to just let me have him.

he has really bad clamped fins, and he’s getting some stress striped bc he used to be full white. i wouldn’t be surprised if he has ammonia poisoning. i plan on putting him in a pretty bare hospital tank when i get home. i have a cycled tank so im going to take water from there. and i have methylane blue so i could do a bath. i’m worried bc it’s about a 45 min drive.