No, I'm not, what she said is extremely clear unless you think she never had a teacher in her life despite being in middle school.
The rest of your comment is irrelevant because it's in the realm of fanfiction at this point.
She literally said, "Thank you very much, again and again, you have helped me, and taught me a lot."
So, no, she didn't explicitly say thank you for some explicit thing, but she did implicitly thank him for educating her, after they discussed her getting into college, so there's an obvious connection between her discussing his tutoring helping her get into college and thanking him for helping educate her.
Afterwards, she directly conveys that she was in love with him, but recognizes he only thought of her as his student, clearly showing she recognizes that they were in a student - teacher relationship, and then expresses coming to terms with that, which she previously had not, and, thanks him for teaching her, expressing gratitude for him being her teacher.
Afterwards, she says, I'll never forget what you taught me, which contextually, is most likely meant to be understood, as all of the things he taught her in their academic and romantic relationship, which makes sense because Meguro is discussing their academic and romantic relationship...
So, no, the whole comment makes complete sense, and none of it is irrelevant.
Your comment is actually what doesn't make any sense...
But I get it, you have to say something like that, because you cannot actually make a legitimate argument.