My experience with Troxels has always been positive. I find that they fit people with more ROUND heads better than folks who have more oval shaped (longer front to back, narrower at the sides). I am ovalur, so I use a Tipperary.
However, looking at the website, since you are buying one without the benefit of fitting it to her head, I would Definitely recommend the Aegis because it has the DIAL fitting mechanism. These are great for making the helmet fit snuggly and this is the most important factor. Also, a young girl will like the shiny pretty colors more. The more you like your helmet, the more willing you are to wear it.
You can put cool stickers on it, too.