I have to say I'm always wary of the settings where magic is restricted (in the sense the only who can physically use) to nobles. Not by itself, but mostly becouse it seems arbitrary, false.
A mean if a setting magic is restirected to priests and paladins, it's easy to contextualize into a form of Divine power.
If the restriction is that only noble can use it then tihs kind of contextualization is way more difficult, becouse informations are missings. There is a system in place that grant a title to commoners that develop the ability to use magic? There was a purge that eliminated the commoners with magic, so that the only one to keep the magic traits are nobles? What about other worlds countries? (assuming that the settings have multiple countries with differences).
The smae thing applies to the settings where magic users are present only in one country. Why that one? What do trigger the magic appearance? Location? What about descent? Have magic only the descendant of natives? Or also immigrants? What about border increase decrease? Are magic user appearance the same probability on the entire country?
A lot of other questions can be asked.
It's important to contextualize and give a proper shape to the magical system, and allowing understand on who and why someone can use magic is part of it. Now I don't ask a system where everything is planned down to the last spell, but a little of planning and consistency is nice.
In this case Finne can use magic becouse "surprise both of her parents were nobles". Me : GENIO! (In a strongly sarcastic tone of voice, (this is actually a quote from Boris a satirical Tv series about the italian televisive often nonsensical productions). Followed by a "Bestemmia"
Note it may also be avoidable to tell everything to the reader immediatly. It can be taken slowly, in some cases it's possible for the characters to actually discover some "occult past" (in sense of hidden, secret knowledge) that made the country magical system as is, togheter with the reader.
Settings were there isn't a precise distinction have a lot less problems in this sense (a couple of examples, magic need precise knowledge that most commoners can't afford, so very few or none commoners can use magic directly, or noble families are a way higher chance to have magical descendant respect to commoners (without other infos I would suspect nobles families tending to marry eachothers when not directly inbreeding ) )
However even them can use a bit more of planning on the systems (not only magical systems) to be a more differents and stand up more
