Her jumps only work when she has minions around to autoattack. Try to get the Q on her when she isn't autoattacking and jumping around. This can help you engage on her, but it won't help if you're already fighting.
Another thing to note is that she jumps further when she is going backwards. If you engage onto her and you think you'll win a fight, then you should prevent her from escaping by standing in her escape route (for example, if you go on her in lane, stand closer to her tower than she is. Your E can help you reposition for this). If she autoattacks you to jump while running away, then she'll be jumping towards you, which will lower the distance she covers. This is mainly a laning technique, as it can sacrifice too much positioning to attempt in the later game.