Totally stupid. I would totally have bought into April wrecking a few Foot Ninjas, and I'd much rather see Karai fight one of the Turtles or Splinter anyways.
I guess they just had to submit to the tropes of "girls must fight other girls" and "the good guys always win".
And the cost of, oh I don't know, any possibility of us taking the Foot or Karai or even the movie itself seriously.