I think that it may not be as much of a height thing, as a skill thing. So she's skilled at hitting people easily 'cause she's tall. Still a skill.
I found that one of my students would not attack the other students because she was more skilled than they were. I'm sure she was thinking the same thing, that it wouldn't be fair, that she wanted to be nice to them, etc.
I came up with two ways around this, for two reasons.
First, I put her on a team. That way there were other people counting on her to perform. It wasn't just about her, and whether she cared if she won or lost anymore. There was a team that she couldn't let down.
Second, I gave the less skilled fencer only 5 points to win, and doubled the amount she would have to get to win. It still wasn't murderous, but she got the idea and fenced better.
The first reason that I did this was because she was not learning anything by standing around waiting for the other kids to hit her. She was just being nice, and as her coach, she's supposed to be learning something. Niceness is mostly for in between touches/off the strip.
Secondly, it wasn't helping the other fencers either. All they were learning from fencing her, was that they would be able to walk in on all their attacks and that things would be easy. It was not a good way for them to practice.
When people just stand around and wait to be hit, what happens to tempo, footwork, and that general rythm of fencing? It just DIES, and it's not pretty. They don't "get it" either. Not in that bout, and not when they go up against someone better than them who's serious.
Oh, and from one tall girl to another, respect your height, appreciate it and stand up straight. It's not going away, and people admire you for your confidence.

AF