When she is sparring or moving at all really, 1/30 second shutter speed will usually give you blurry shots at 50mm. You will probably need to increase ISO and get that shutter speed way up if you don't want to use flash.
However, a little motion blur can be great but only when used properly (like the fist and arm slightly blurred but the boxer sharp, showing a punching action)
What scared me off was going above 1600. I asked her if we could revisit some shots. I am going to bump to 1600-3200 and bring my shutter up to hopefully 640. 2.8 is the sweetspot. I will take care of some of the noise in PP. I am learning, I am learning.