The best shot at taking down malenia starts with getting your vigor up to at least 40, and equipping something that can proc bleed damage like rivers of blood or dual katanas. If you're comfortable with your dodge timing that's great, but bringing a high stability shield isn't a bad idea for those tricky waterfowl dance moments. Speaking of which, when you see her jump up for that attack, you'll want to walk left first, then dodge forward through the first wave, backward for the second, and into the third one.

Getting a mimic tear maxed out to +10 makes a huge difference, just remember it uses your hp to summon. Make sure to equip your bleed weapons before summoning so your buddy copies that setup. Once you hit phase two, the moment that cutscene ends just sprint away from her dive bomb, and consider keeping flame cleanse me ready for that rot buildup.

The real key is staying patient and not getting greedy with attacks, since she punishes that pretty hard. Frost weapons work really well too especially paired with bleed, and don't forget to stack some defensive talismans like dragoncrest greatshield. If you're still having trouble after a few tries, summoning other players is totally fine just keep in mind she'll heal whenever she hits anyone, shields included. The fight gets way more manageable once you've got the rhythm down and aren't rushing your attacks.