I think in order to understand the (admittedly frustrating and disappointing) 'suicide pact' plotline, we have to unpack a couple things about both kali's character and kali and el's dynamic, so just hear me out...
1) kali is, in a very backwards way, at the heart trying to protect el. that sounds antithetical, but this isn't some maniacal plot to drag el down with her. kali has just gone through unimaginable horrors - she watched her friends die in front of her, she was stripped of her personhood to become essentially a machine that pumps out blood, forever caged and drugged through it - all at the hands of the government. kali witnessed upclose kay's cruelty, and then stumbling upon those mothers, saw behind the gov's curtain. she saw the end of the tunnel, and there's no way out. so she a. wants to protect el from being forced into what she had to endure, and b. save those mothers and potential babies from going through what they had to in the lab.
2) it's also important to remember, that kali's mission has always been about justice. it was always about remaking what was wrong, and taking those responsible down. for that to happen, to protect those potentially hundreds of kids and moms, she believes they must sacrifice themselves. it's so important to her that this never happen again, that she'll sacrifice herself for it.
you gotta remember where kali gets her name - from the goddess. the goddess of both justice and destruction, but also, of mother love and protection. our kali is the embodiment of all these things; wringing out destruction and justice, but at the heart of it, it's because she's trying to protect others. she was trying to protect potential future victims by killing those lab-workers, and she's trying to protect those moms and babies by giving herself up and ending the cycle, as well as protect el from the always lingering possibility that the military could snatch her again.
and 3) in the very short time we got to see kali and el together, they have been at odds with each other. they have many similarities and it's clear how much they care about each other, but they're very different when it comes to their outlooks. kali believes ridding the world of those men who abused them is bringing justice and stopping the violence, but all el sees is blood - and that's part of why el leaves. and once again, it's clear that kali is hung up on another idea that el just can't get behind; I don't know about you guys, but all through their conversations I could really sense el's hesitation - even at the last scene where they nodded to each other. I'm thinking that either el changes her mind later on and convinces/tries to bring kali back with her, or she's flubbing to her sister so she can try and save them both later. bc el has always carried a spark of hope with her, within that big heart she has, which I think kali either lost a long time ago or it got swallowed up in her anger. I'm really hoping, el is able to give that back to her.
another small but key thing about kali, is that she's incredibly single-minded. she's nuanced and very smart, but clearly always been someone who jumps in head-first when she commits. she's on this justice mission full-heartedly when we meet her, and committed to giving el the same kind of 'relief' it brought her to kill their abusers - even when axel tells her the mission is too dangerous, kali pushes it anyway. whatever it takes, she'll make it happen (a lot like el that way..)
(also a reminder, that kali’s plan didn’t work out the way she wanted; el stopped her from killing ray and then they got caught. maybe this one won’t work out either!)
to top it all off, kali is unbelievably traumatized from what happened to her, and suicide is a common response to that. while I don't love that the writers are making her push this and therefore putting her at odds to everyone else in el's life, I can see why it's happening and why kali is so adamant about this, from a character perspective.
the final is going to be a long one, about 2 hours worth - that’s plenty of time for el to hopefully bring her sister back from the brink 🤞🏻