Obviously a lot of what was written in that letter was totally made up, but there's some fuzzy ground here because of the long lifespan of elves and some blank spots in her character background. She had a window of 20-25 years to complete her formal training before she left the elven kingdom, and then 40 years in the human kingdom of which a good 30 of them were spent in the Nossari capital. Anyway, upon a second reading of you wizard spoiler in the OP, I may have been using the term incorrectly.
My intent was that she be a low level "journeyman" rank wizard. I was intending the term "librarian" in the context of "works at the library." She wasn't a student, but she certainly wasn't a "master wizard" either, but she would obviously have been a useful participant. I didn't go into much detail about that period of her background, but I can't imagine an elven wizard/scribe/linguist living near the wizard academy/library at the capital for thirty years without being involved with it in some capacity. I'm not really sure what her title would have been. Librarian just seemed a reasonably close approximation.
What would you call a postgraduate wizard who regularly hangs out at the wizard college, who isn't a journeyman of the wizard college because their training happened at a totally different school in another country...but who is a professional scribe and linguist who speaks five languages, and offers copy and translation services either on a paid or totally volunteer basis because she has a lot of spare time and can't exclusively hang out in the court 7 days a week, probably offers elvish language instruction because she's a relatively rare native speaker and again...has a lot of spare time, probably isn't a formally acknowledged instructor of magic because she's not high enough level and doesn't hold the rank of master, but would be ok with teaching what she knows if anybody cared to ask her to, and happens to be older and has been around longer than some of the formally acknowledged instructors because she's an elf and has been slacking around the place for thirty years?
Actually...I think I have our answer. From the OP:
Apprentice: an apprentice is studying under another wizard (usually a journeyman but perhaps another rank) in preparation for enterance into a library. It is generally considered an incredible stroke of luck to be selected for an apprenticeship. It's possible to enter into an apprenticeship at any age but generally a wizard will only take on an apprentice who has something to offer. It is possible but rare for private tutoring or self-education to replace an apprenticeship.
As a journeyman wizard who spent 30 years hanging out at the library a couple nights a week, she probably took on a number of apprentices during that time and offered tutoring. She was an instructor of apprentice ranked wizards in addition to offering transcription/translation services to the library itself, and this would be something she did part time, averaging about 2-3 nights a week over 30 years. What would her proper title be? Instructor? That's more prestigious sounding than I was intending, but it fits the scenario.