I'd say that it's a cause for concern, even if it isn't stringhalt. Her movement is still irregular at some points (especially when she comes around the northwest turn of the circle), and it could be anything from mild soreness or lameness, to something more serious like a fracture.
It's good that you've noticed something is off and that you are getting a vet out.
Here's a helpful webpage on stringhalt
, for further reading.