I think you are right about this. The sisters/girl power thing really caught on, especially with Idina Menzel's Wicked-esque voice influence, which of course had a similar message.
Also, and I know it seems farfetched, but the winter in which Frozen came out was especially brutal in the northern US that year. This let to lots of folks sharing video of their kids singing "Do you want to build a snowman", etc. and generally fed into the Frozen frenzy. Honestly, I'm not sure the movie would have done as well had it premiered in the summer.