I was quite proud at this moment actually! So proud that she jumped in the way to save Twilight (even though it was probably the glancing blow off Rainbow Dash flying REALLY fast...)
Although, I have seen the movie twice and in both versions, the actual line which precedes the "Freezing" was actually different! The first time, there was a voice (NOT Rainbow Dash) which shouted "Princess!" and then you saw the frozen Muffins. In the second viewing, it was "Twilight!" that was shouted, and it sounded like Rainbow Dash. Although you could still see that it was Muffins being frozen in the orb. If it was Muffins, one would assume it was her that actually shouted "Princess" rather than "Twilight."
I don't know if there's different edits going about, but I swear they were different! Can anyone else confirm this?