The Dragonfly has three drawbacks here.
Firstly, I don't think you'll be able to reach that height with it from the ground. Secondly, I find that, if you have very dustyglazing bars or frames, it drags the muck onto the glass and causes an even bigger mess. And finally, the system is only, in my opinion, effective as a maintenance cleaner and really strugles with a very dirty window.
Personally, I'd do it by trad off a scisor lift.
Goos luck