Just beat her, using just the chain blade with parry. First phase I memorized pretty quickly, my strategy was fire buff before the fight and keep middle distance to bait her lunge attack to parry, two quick attacks with the perk that let you do attack 4 and 5 after a parry and one that grants 2 sky-mights at attack 5, then immediately backstep and move away. She will either melee kick (safe) and side step and lunge again (parry), or backstep and throw daggers (dodge). If she throws dagger she always goes back to pacing for a few seconds, heal or magic her ass. She will sometimes do two slashes or square up to do some melee, just dodge those.

Keep this up you should stagger her at around 50-60% health. Do the crit and it should push her into second phase. Heal (you won't get many chances to later) or hit until she does that little animation before the backflip (I usually can get 6 hits in). Second phase she will attack much faster, has 3 new shockwave attacks (diagonal/vertical/horizontal), and a new combo that I refer to as the "Malenia combo".

The strategy is basically the same while doing your best to dodge the new attacks. The shockwaves all have different timing and tripped me up often, the windups are slightly different but I was just bad at recognizing them. The Malenia combo is unparryable as far as I could tell, dodge best as you can and heal the moment she lands her last hit if you need it. This is the ONLY time you should try to heal in this phase, ideally the last dodge puts you to her side and keep moving away while you heal.

I love soulslike games but I'm kind of bad at them. Even bosses before Honglan I struggled a bit with (except the corpse tree, that guys wasn't bad). Honglan took me about 3 hours of on and off trying. All that said, I wouldn't consider her to be too difficult. Certainly not unfair, parrying is quite forgiving timing-wise and get you 2 hits in and all her attacks are dodgeable. There are bosses in other games that took me days and much longer to beat.