The series is set in a dystopian society where everyone takes a test at 17-ish to determine their “number” which determines their place in society. I think 7 or 8 is the highest but only the founding family is the highest number. The main character has never been able to read and so she gets a really low score and runs away to become seemingly a prostitute but is “bought” by a member of the founding family because she resembles his dead niece. He drugs the girl and she wakes up wrapped in bandages and has been surgically altered to be identical to his dead niece in order to keep the public from finding out she died.
There are 3 or 4 novels in the series.
Possible plot spoilers:
The dead niece turns out to be alive after all and was leading a secret rebellion to take down her family and fix society. In the society, level 1 people are like the disabled or mentally handicapped and they are presumably killed. Also, elders are eventually also sent away as well. The main girl finds out that the place they’re sent to is actually somewhere that the founding family goes to hunt people but that’s honestly just a small side plot.