I'm looking for a YA fantasy novel I read a while ago, probably in the 2000s-2010s. I'm pretty sure it was the first book of a series. The main character was a teenage girl in this magic society where everyone would get a pocket watch (?) at a certain age denoting their magical rank (i.e. strength) and amount of magic they could use. Each section of the watch was denoted by color, and the amount of magic represented increases exponentially with each section. Every time you used magic, the hands on the watch would tick down, and once it reaches zero, you're out of magic for life.
The main character turned out to be very underpowered in terms of rank but overpowered in magic quantity, which of course leads to people looking down on her (including a rival who has a super high magic rank?). I don't remember much else about the plot, other than how the MC used up a lot of magic by the end of the book to make an enchanted item and other spells.
I think this took place in a forest setting.