there's not much point to beating the Fremmy fight since it's the end of the remake but you can mostly cheese the fight by moving diagonally and only hitting her once before backing off while she launches a barrage of attacks.
If you keep getting hit or she does that fucking sliding move where she blitzes across the screen and hits you no matter what your best bet is to buy a bunch of soft drinks and is it gum or something? I can't remember, the fucking healing items but like 20 of each and whenever she knocks you below half health just run around for a bit and get a little distance and then heal up.
It can be a bit tricky learning the right input to use the healing items while she's chasing you but if you buy enough, you aren't greedy with your attacks and you heal before your health drops into the danger zone you should be able to clinch it easy.
It took me 4 tries and the 3rd try was just me figuring out the best timing to use healing items since I didn't have any before.
TL/DR
USE HEALING ITEM SPAM TO WIN!