Hi,
Was PU/PD your first course of action? Here is an excellent resource for PUPD... especially adaptations. If I remember correctly, the ideal phase for pu/pd is around 6mo-10mo or so, then adapted for older kiddos.
https://babywhispererforums.com/index.php?topic=275699.0I would set a time limit of 1.5 hrs max for sleep help efforts. So if you're trying to settle her after a 40 min nap, try for another 30-40 mins, and then stop. After a few times of PU/PD, try a lean in and pat approach where you're so close to her, like hugging her, and gradually withdraw your touch. I used PUPD along with GW... so started with PUPD, then went to patting (less and less of it), then staying in the room and saying comforting words, etc...
Yes, I would stay with her and every day move a little farther and farther away from her bed. The second she calls out for you, go to her and pat (not pu/pd) and see if she settles. After a few days, don't respond to her right away, but count to 5, then 10... and so on. (Unless she is full crying, then go to her and respond either with a pat or comforting words).
I'm sure you've read about all these methods, but just a reminder that you might have to adapt and include other ways since she is much older. My son responded well to key phrases eventually... "It's sleepy time. Mommy is right here."
Hope that helps!