Since she was free and in her paddock when she did the rearing it's possible that she was either playing or telling you to get out of her space. If she was playing, in the pasture on her own the rearing isn't that big of a deal - as long as she doesn't do it while you are handleing her or riding her. Now, if it's more of a get out of my personal space issue then it's something that needs to be dealt with. Since it was the first instance it's hard to make an assumption on her actions too quickly...
PS - I don't see the video... :(
"Be a best friend, tell the truth, and overuse I love you
Go to work, do your best, don't outsmart your common sense
Never let your prayin knees get lazy
And love like crazy"