What are Erasers in the books Maximum Ride?

It doesn't say specifically why (because i don't think James Patterson knows where he is going with his books) but I think it's because Angel is super special (even though i hate her). She has special powers and they needed to experiment on her (hence the name Angel Experiment).

I hope I'm right, but this is just an educated guess. I've read the whole series about 4 times and it never says specifically why they kidnap her in the first place