Oh, sure. I can make it happen even as we're walking.

[Lightly, she gestures to the side, but while keeping her hand into the proper shape for casting. Might as well let the new girl see what she needs to, after all. With that done, as she's skipping along, she slices her hand along through the air-]

Line!

[And there's a bright and fairly sturdy borderline up alongside them, on the right side.]

It looks simple, but some people seem to find it tricky. So I guess it depends!