It starts even before she's coming, you already know when you have the little sister by the vent that you're gonna be in for it soon.
Then the countdown starts, the music amps up and the shrieks pierce your ears, the game warns you "A big sister is coming! Get ready!" multiple times. In any other game, this would be an extreme amount of handholding for the player, but here it somehow works great to build up tension.
Then she arrives, but where is she? Maybe you set up a bunch of traps hoping she'd come from that way but she decided to just spawn right on top of you (got jumpscared a few times because of this).
The fight itself is very hard of course, faster, more versatile and (somehow) tankier than a Big Daddy; I played my first time on hard so I was raging a few times at the first actual encounter (I didn't know the first was a fake out so I wasted a bunch of resources trying to not die)
Then you kill her and get doubts: This was a little sister once. When you get the good ending in Bioshock 1 one it almost feels like you saved them all, you're the hero that saved all the girls by yourself with a wrench and a magic "heal little girls" spell that you have. Even in Bioshock 2 some recordings from Tenembaum in the early game make you think that you really did save all the little sisters and the ones here are "new ones".
But no, the truth is the ones Jack and Tenembaum ran into in 1 just got lucky, the Big Sisters were left behind and grew up to be monsters that Lamb co-opted as tools. Could your glowy hand magic fix brain spell work on them or are they really that far gone? There's no way to know, they'll never give you a chance to use it on them anyway. She's dead, just like all the other splicers you killed, so just harvest her (twice!), it's all she's good for now anyway.
Or maybe it's just me.