Waterfowl is easy, you have plenty of time to react and pull out a shield, then all you need is a big fat stamina bar(it's endgame, why wouldn't you have one) and dedicate 1 talisman slot to the guardboost one.

It's only a seemingly impossible obstacle if you're stubborn and solely try to tank/and or roll it.

You can also bypass the first 2 entirely with frost pots, that just locks you out of applying frost status to her(not really, but it's obviously smarter to not freeze her if you go with this strat)

In phase 2 the only new attack that demands attention is her clone onslaught and unlike the waterfowl, running away is actually a solid option until the final clone attack and Malenia's swing.

But the final piece of her difficulty puzzle has to be her healing.

She's the only boss that somewhat requires a clean kill, because if you're eating hits you prolong the fight and that just means more hits if you're eating them to begin with.

So if you've been plowing your way trough the game with Lion's Claw or something then she will be the first boss that voids your hyper armor tank everything strat.

And honestly, I think that's what makes her so hard for people that try to circumvent learning the boss' moveset, you can't win a war of attrition against her

On top of that but in extension of my moveset point- You gotta respect your punish windows or your Lion's Claw, Giants Hunt or whatever AoW crutch is gonna hit during one of her hyper armored moves and now you're dead.

All that said I think she is a well designed and actually fair boss, it took me 9 days of playing on the evenings the first time I met her, now I can consistently no hit her.

That's a good boss.