All Diana really did was use her armor to block and throw Cheetah around until they fell in the electrified water. Alita will chop her to pieces with no hesitation and her berserker body using panzerkunst should be more than sufficient from the barely 2 minutes we see Cheetah actually fighting. Plus she's shown no resistance to the Damascus Blade's cutting potential.
I'm not saying she isn't formidable. I'm saying she fought Diana who was holding back and didn't use any lethal weapons against her. Alita has what is essentially a lightsaber and would herself be able to hang with Diana for a while with a mix of skill, speed, strength and durability. Cheetah can't block any of the sword swings or try to catch the blade. She'll lose whatever part she tries with.