Upon closer examination of the sample video, she is not writing what you are seeing, her movement only approximates the motion and if you look close enough you can see it is a mime--take a good look at the "E". She is not moving correctly to get that "E". I don't know what resources you have to work with, but if you want to copy this technique you need to have 2 things:
1) an actor that can closely mimic the correct motion as if she/he is really writing.
2) a good post production video editor so you can animate the writing content on a separate video track and make a composite.
Hope this helps
ps, by the way I think the actor in your example did a marvelous job of miming the motion to trick us into believing she was actually writing the text on glass.