I am going to attempt a royal icing tiara for my daughter's birthday cake.

What is the best royal icing for this?

Thanks in advance for your help!

I was going to do one but I run out of time. When I did a search for tiara info on here I found that most people said the RI with eggwhite is much stronger and that those who used one without eggwhite had theirs crumble. I decided to do a gumpaste one but I didn't leave myself enough time and tried to rush it and pulled it off before it was properly dry and it crumbled. Not happy!

In case you experience serious difficulty (like I did), here is a link to what tiara I had to finally use since nothing was working and I was totally out of time. I made it out of fondant. http://www.cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1424453

I use the recipe in the Wilton meringue powder. It come out great every time. It is mostly powdered sugar with some meringue powder and water or flavor. It has both a regular and thicker recipe. I used the thicker recipe.

FYI - the extra makes nice after dinner mints with some mint oil. The recipe makes a lot of royal icing.

For a tiara, I would make royal icing from raw egg whites and sugar and add some white vinegar for strength (about one to two teaspoons per egg white).
Mix it well, don't beat it (use either dough hooks in hand mixer or paddle in stand mixer. After mixing, let the royal icing sit covered either with kitchen wrap or damp cloth for about one to two hours - it needs to be covered so it doesn't crust. This way, all the small air bubbles can rise to the top.
All this should make the royal icing stronger.
As for the tiara:
Make two or three so you have spare if you can. Althrough you can almost always glue the tiara back together with some more RI, sometimes the break is in very unfortunate place.

Good luck to you.

Thanks for the tips!