It is totally fine as long as she agrees that you can do it. I am 18 yrs old and my boyfriend has been spanking me for discipline reasons for the past 6 months. While I agree that I need it, and I actually am the one who asked him to do it, I dont necessarily like being spanked. It hurts alot, but like I said, I agree that its necessary. I can be a brat and I do go out to parties where ill get wasted, this is precisely the time where I need a firm hand and MAN do I get it! The point is that she might not want to be spanked but if you believe it is necessary then sit down with her and talk to her about it, she may agree if you explain it to her. She may even realize that she does need it. Just be honest and let her know that you still love her and thats why you are taking the time to find ways to fix her behavior problem.