What's the Name of That Book??? discussion

I haven't read this book, but I think it's a classic because I vaguely remember multiple pop culture references made to it (but not who made them or when, sorry).
The character had a geographical name I think, my first thought was Oklahoma but that didn't turn up results, and a major aspect was that she only had the memory of a regular human, and had to write everything down (in books?) so she wouldn't forget over her long life. That's the only thing the references mentioned so I assume it was one of the most important or noteworthy aspects of the story.
Apologies for the sparse information, I just incidentally referenced this book in a conversation because I thought it was well-known...but realized I didn't know its title, Google failed me, and now it's eating me from the inside out.
Anything helps! Thank you in advance.

Anomalie, around what year did you discover this book?
Is this book for adults or teens?

Story's time period(s) and location/ country?
When and where was the woman born?

I'm sorry, but I don't remember anything else about this book - I assume it was aimed at adults because I don't think teen/YA was really a "thing" when it was written, which I also don't know for sure but my instinct/vague memory tells me was likely pre-2000 and possibly quite a bit older - I feel like it might have been one of the first well-known stories about immortal characters living normal lives, since...if it was written in a time with a more saturated fantasy market I don't think it would've been as remarkable as I believe it was.

This is a bit of a long-shot, but it reminds me of The Crystal Singer trilogy by Anne McCaffrey. The crystal singers are very long-lived but the crystal singing affects their memories so they have to write their memories down, which is particularly important to the third book. It's a SF rather than a fantasy though. The Crystal Singer Omnibus

I FOUND THE BOOK: Orlando, which explains why I was so convinced the title character's name was a state and definitely has enough letters in common with Oklahoma that I don't feel like too much of a fool for guessing that.
SBC, thank you for your guess though, she's a favorite author of my childhood so I'll have to check it out regardless - since the book I was looking for wasn't just "pre-2000" which was my just-in-case-I'm-wrong-about-it-being-old guess but was written in the 1920s, there's a chance the Crystal Singer series picked up that idea from a grapevine Orlando planted, even.

Orlando makes more sense with you remembering it as a classic! I'm glad you found your book :)