She was a brilliant sleeper and was no trouble getting to sleep
Then you should be able to get back to that, don't worry. And no need to get everyone stressed by leavibg her to scream.
I would start with some in-cot settling. Is your partner around at bedtime? While the aim would be that settling her to slerp takes 10-15 minutes, initially it might take 30-60 minutes. Ideally it needs you to be able to focus on baby, with someone else sorting out your other two children.
So start by bending into the cot, firm hand on baby's chest/back/shoulder. Don't push down, byt baby should feel thr weight of your hand. The idea is that baby can close her eyes and still feel that you are right there and going nowhere.
So lean into cot, firm hand, some patting and shushing as needed. Stay until fully asleep, don't stand up or move throughout. Seek out once fully asleep. Repeat any wake up.
Get this established do she trusts you'll never sneek out too soon and you'll alway give reassurance until asleep. Once she trusts you to stay, the battle to stay awake (in order to keep you there) stops and going to sleep gets quicker. Expect less than 15 minutes.
Then start reducing her dependence on reassurance. So lean into cot with firm hand to settle. Stand straight up when calm. Return to leaning in with firm hand if upset, always withdraw when calm. Stay until asleep.
Then settle initially but take a step away. Return firm hand if distressed, withdraw once calm. Stay until asleep.
Then stand by door when calm. Then stand outside of door once calm. And so on.