Grab a pen, a piece of paper and do trial-and-error.
You'll be wasting your time unless you use cheats though, Sabrina has a full Lv255 team.
She, just like the other Kanto Gym Leaders, is meant to be rematched in the endgame of the hack.
Yes, Only Way I got around her was with savescumming and Marin + a team of Protect + leech seed+ whirpool+toxic spammers. Also endeavor works really well when the lvl-hp difference is so massive. Some of the pokes gave 11k exp LMAO, and Mrs. Mime was a fun adition to the comp.
The one that was really a pain was Venomoth as giga drain goes through Marin and you cant poison it either. Also this fight let me see that poison sometimes gets bugged with leech seed and or whirpool, poison stops working and when the alakazam was trying to hypnosis my team, i dont know if it was Dragonair's shed skin that bugged it but suddenly i was in and out of sleep on every pokemon and the team got sleeped even when they weren't attacked by hypnosis. Weird.
Yeah, I don't know how but I ducking messed up my file. I was using the emulator VBA (SCONGVIT). Don't know if that's correct or not. I reached Sabrina, got defeated. Saved my rom hack. Loaded up again and I started at the beginning. Like wtf. I lost all my hours of hard work. @Lunos you also have bonus chapters playlist on YouTube right? I'm fcking done now.