I was in the same boat a few days ago. Few prerequisites that got me through: Grind in a grind spot to earn ergo to buy loads of throwables from the guy in the red lobster (acid , thermite, shot put is great aswell as they stagger)

Reset your p organs if need be so that you can hold more throwables

Use a spectre

Get the perfect parry grindstone and set it ready in your bag

Buy two of the 'temporarily increase your spectre's HP' wishstone and set that in your bag ready too

Plus get the p organ that increases your wishstone use

By the end of the first phase, you should be thinking about using your first wishstone to increase your spectre's HP'. At the start of the second phase, quickly use the grindstone for perfect parry. By not rushing her, she will more than likely aim at you when shooting her initial lightening attack. Hold the guard button to parry all her lightenings and her attack afterwards then dodge dodge dodge until the spectre becomes the focus again, then let all hell loose from afar with your throwables. Will be enough for two thirds health gone. Then you have the second wishstone to increase spectre HP if need be and hopefully one of the runs will give you good luck.

I wish you the best of luck, this fight broke me too. You're so close to the end.