My daughter, who just turned three, hasn't been open to re-direction, especially for something she really cares about, for quite a while now. That really only worked when she was very small. What she DOES respond well to is a firm but gentle No followed by me telling her why and then when I would be okay with her getting what she wants, if that's appropriate. So if she wanted to nurse when I didn't want her to, I just said No, Mommy needs to rest, but you can have num nums at such and such time or place. She may protest, but with consistency- not giving in, and always giving it to her when I promised I would- she accepts it readily enough. I do this throughout our day for lots of things, and she usually just sighs and says, Okay, Mommy.
Another suggestion that worked very well for us was designating fewer and fewer places that she was allowed to nurse. So when I am fine with nursing her, we move to a certain chair, for example. So me sitting in that chair is a signal to nurse, and if I'm not in that chair it becomes obvious I will not be nursing her. It eventually became only okay to nurse in bed, side lying, so she quickly stopped trying to nurse elsewhere, and when she wanted to nurse, she asked to go to bed. Me sitting down stopped being a trigger for her, so I was free to sit down!
I am pregnant now, and in my third trimester, and I ended up weaning her right after her third birthday. My policy was always to maintain a nursing relationship that we both enjoyed. My decision to wean her was very tough, but I found myself hating nursing (dry nursing with serious pain), and the last thing I wanted was to start resenting her instead of connecting with her. Looking back, I am very pleased with the course of our nursing relationship!
I hope this helps!!