Because the Crystal can't be destroyed, and Usagi has a much larger versatility, Yuna can't win.
However, I'd like to ask the opposite of Galaxian, actually. What does Usagi have to incapacitate Yuna? Her body is untouchable and anything that would harm her is automatically blocked. The most Yuna has been seen unconscious in a fight was only 2 minutes or so, very far from the 1-hour-requirement for SBA. 5-C Usagi doesn't have any reality-bending or mind-related hax yet, either.
Yuna won't touch Usagi, bc of her crystal, Teleportation, Healing, beam spam and range (or will have too much of a hard time). But Usagi can't harm Yuna in any way physically bc of her Type 4 immortality, coming from a 3-A being. Also, both have huge stamina, and will very likely quickly recover from any sort of unconsciousness, so they'll just continuously keep going at each other.