Anyone actually know why she was recording the police? (apart from because she can, thats not a valid reason to record anyone)
No, it's not mentioned at any point. Usually when people film the police it's to make sure they don't do anything beyond their powers.
And to Spanky:
The officer had no need to order her to move further back, until he approached her, she was well clear of the proceedings. And he wasn't asking her to move further back, he was asking her to go inside, which would obstruct her view of the proceedings significantly. She was in no danger, and she was posing not threat, the police had no cause to order her back, and certainly had no cause to arrest her for not doing-as-told.
On top of all that, when she finally agreed to move back (which she didn't need to do anyway), he still arrested her.