Initiate (A Spell for Kia Book 1) by J. P. Larson. Kia age 12.
Novice (A Spell for Kia Book 2) by J. P. Larson. Kia age 14. Her happiest year. Almost nothing horrible happens to her.
Apprentice (A Spell for Kia Book 3) by J. P. Larson. Kia age 16. Kia is locked in a room and given absolutely no choice but to sign an eight year service obligation for her apprenticeship. Later she learns that students that advance that far but refuse to continue get their magic burned out and usually die horribly.
Journeywoman (A Spell for Kia Book 4) by J. P. Larson. Kia age 18. Getting dumped sucks. Body snatching witches are bad.
In a world where sorceresses are exceedingly rare (less than two hundred in the kingdom, including students of apprentice rank and up) Kia is essentially kidnapped from her farming village at age twelve and imprisoned in the Northmere school of magic. All the other students are honored to be there and can't seem to understand why she's so upset. Even though her magic is pretty much useless, she has so much of it that there's no chance they will ever let her go.
This series is your standard "growing up in a magic boarding school" with a dash of grimdark. There are plenty of twists, turns, and sudden betrayals. Each book advances by about two years as she grows in power and skill and goes up in the ranks. Hopefully its not over (there are at least three more ranks, Adept, Magus, Senior Magus). I'm pretty sure J. P. Larson is also Robin Roseau.