How do I turn of my ability to see if someone read my iMessage?

I know there is a way to turn off the ability for people to see if I read their iMessage. However, I have. A friend I'm talking to that has that option on and it can drive me crazy sometimes. A lot of times, she will respond, but there are times she won't. What's annoying is seeing the "read" right under the message I send. I try to let it go, but still annoying. I would rather not know if she read my message. Is there a way of turning that off without asking her to do it.