I don’t know why you think she’d have a 1st amendment case; intentionally obstructing public passages is a crime in PA. Time, use, and manner restrictions are widely understood to be constitutional as long as they are content neutral and do not restrict expression. If she was following behind or in front of the robot with a sign, that would be one thing, but intentionally blocking someone or something almost certainly does not constitute protected speech in itself.

This being a motorized vehicle on a pedestrian sidewalk, that "widely understood to be constitutional[ly protected]" is a stretch.