I have a hard time believing that Tripope's love will save her - unless you mean Tripope as Tripope loving Yordlah and not Luang Thep. If that's the case, that's an angle I never considered.
However, the reason I don't believe that finding out the truth of who Luang Thep really loved will save Yordlah is because, based on the assumption that the one he loved is Dararai, finding out will only seem like betrayal to Yordlah, and Yordlah's already furious because she thinks everyone turned on her: her sister, her father, Luang Thep's family. Finding out that Luang Thep really loved Dararai could only make it worse. There's a chance finding out might make Yordlah wake up and realize that she's spent two centuries fighting for a man who didn't want her and she'll just...give up, but given that so far, she's blamed everyone for her bad life, it's equally possible that she might chalk up the misunderstanding (stupid Luang Thep) to him deceiving and betraying her. Which was why I initially thought (before I started the lakorn), that it would be the bond between the sisters that saves her because deep down I'm sure she still loves Dararai and that despite everything, Dararai loves her, and when Yordlah realizes that her sister didn't technically betray her, she'll remember the love and the feeling of being loved and repent, which will save her from eternal damnation. Now I'm not so sure since they've downplayed the sister's bond so far. At the moment, I can't imagine what would bring Yordlah back to the good side.
It's also significant that Pimdao remembers and hears the song when Pinky plays it, not just Tripope. I don't know if Mo made a mistake, but since the scene "passed," I can only assume that either they didn't notice her gaff or she said it correctly and it's supposed to be a clue because in episode 8, when she heard the song, Dao woke up and cried, "It's the Duang Dao song!" Up to this point, everyone has called that song "Duang Jai." Dao is the only one who has called it "Duang Dao." (On an off note, Thai netizens are confused as to the title of the song - is it Duang Jai or Duang Dao - because apparently it's being called both in the script.)
Anyway, I have a correction to make. I translated the song based on the lyrics posted on Manager Online, but when I went back and listened to the song, they just didn't match up, so I re-translated it based on the words sung in the lakorn.
Disclaimer: I'm not fluent in Northern Thai dialect, so I may be slightly off.
Tonight whose beauty is so radiant and priceless like a star?
She's so bright and high like the moon
I want to tell her she's beautiful, that she's my heart/my dearest
Oh heart! This heart of mine recalls every little detail
I've given her my love and devotion
I hope to spend my life with her
When I dream, all I see are stars
They're scattered across the sky
Its image will never fade from my heart
It sounds so much more romantic and more like a confession. No wonder Pinky loves it so much. And seriously, Luang Thep's gotta take the cake for being the biggest idiot.