I'm going to have a girl send me nudes because I know she has a crush on me
Is that a good reason for sending you nudes?
Yes, I justify my actions considering the fact that she has a crush on me.
It is nice to have someone who has a crush on you, but you should not take advantage of them. You should not mislead them and should be honest with them, thus it is wrong to ask for inappropriate photos of them.
What if I tell her what I'm going to do with them.
I'm not sure what you're planning on doing with her pictures but it'll hurt her if you misused them. Put yourself in her shoes and think how you would feel.