2003 silverado differential?

My sister wa in a wreck and was quoted that her rear differential needed replacing and all kinds of other stuff.. I am a mechanic and have rebuilt differentials before, but i don't generally diagnose problems with them.. anyways the rear end was lifted off the ground and the truck was put in gear and only the right wheel spins and every now and then the left will "catch" and start spinning... is this something wrong with the differential? Perhaps the left axle is broke inside the tube... the left side was where the impact was.. also now her left wheel rubs on the caliper, so it tells me something is off there..