I mean you've posted goodbye horses and one of the best psychological thrillers in my book is Silence of the Lambs. There are goofy moments (and some not great parts about trans representation) but it keeps you reading on the edge of your seat the whole way, and the film does a very good job of keeping you tense.
Also if you can stomach it: watch Baby Reindeer. It's a dark comedy/psychological thriller about a failed comedian getting stalked based on the real life of the writer and main character's actor and it's heartwrenching and shows a victim also making decisions that hurt others while allowing the audience empathy for said victim. Although be warned there are multiple r*pe scenes, so make sure you're in a good headspace if you chose to watch.
I think if we're going to be in this girl's head for it not to be "emo" she basically needs 2 things:
- to think like an adult
- to act like a person
Because a lot of "emo cringe" comes from typical teenage overreactions and overblowing feelings compared to the situation. "He dumped me now I'm BROKEN INSIDE I'M NEVER GOING TO FEEL HAPPY AGAIN I'M GOING TO KILL HIS NEXT GIRLFRIEND" and the like. As someone who's an adult who's been through breakups and watching that sort of thing from afar you're like "ok sweetie calm down eat some ice cream and chill, you'll be fine". Like even though you know it hurts you don't empathise as much because the reaction is so extreme.
That brings me to having her act like a person. We have to empathise with her as she escalates her actions and be able to go "if I were in her position with her background, I could see myself wanting to do that". If the audience genuinely empathises with her then even if she does something we don't want her to, we'll still feel for her.
The revenge blinding all other options is really reminiscent of Ellie's arc in TLOU2 so even though it's not a thriller it could be good for you to have a look at how they told that story.
Tl;dr: if you want to write a psychological thriller that can be taken seriously, watch and read psychological thrillers that do that balance of goofy/serious right and work out how they do it and see how you can apply that to your story.