Riley's been "drunk" on the roof since coming back from the attempt to rescue Lizzie, or at least she's implied to have been. So I doubt she had any interaction with Pippin.
As for shooting the radio, red herring maybe? Riley was fairly insistent about there being another radio. So if the shooter is loyal to the Tower and knew there was another radio, then shooting the radio looks suspicious but doesn't do much real harm to the Tower.
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