Acting O.K, you don't hear any gurgling when the duckling breathes, it's eating/drinking fine (?) I would say leave the duckling be, and just monitor her.
What I'm seeing in the video is that she is possibly a little warm - that can happen when they're all piled up on each other. If you're seeing it even while she's in water, or in cool areas, it possible she has some debris accumulation in her nares, or choanal slit, which is causing limitations to the amount she can breathe in. I do not see anything from the video to indicate she is suffering from a serious problem.