This girl has exceptional good traction.
Slipfactor = amount of handslip/ amount of head forward movement= 10/17.5=0.57.
The avarage swimmer in your local pool has a slipfactor of about 1.5-2 at half the speed.
slipfactor is minimised by low drag, high traction, little speedvariation.
to be more precise, starting point is where hand is definetely is starting to move backwards. Thats ok here, hand is even blurred by faster movement.
the newer, more prcis slip factor becomes:
handslip 12.5 -1= 11.5
head movement 20.5 -4.5 = 16
slipfactor =11.5/16= 0.72
So, worse than 0,57, differnce 0.15, but still..who does it better at this pace?