I'm going to periodically ignore a girl
I'm not sure what makes you want to ignore her. Can you tell me?
I needed to get rid of her
Generally speaking, it's better to talk to someone if they upset you, or if you want to end a friendship or relationship. However, if the situation is really bad, then it can be okay to ignore someone instead of confronting them.
I know, which is why I am going to ignore her and she will be gone soon enough.
If this is what you need to feel better then I am glad that you've figured it out. Sounds like you're moving on from someone you didn't really like, and that is healthy.