This Grandma has it DOWN. She's got some serious moves, is having a blast in her own little world and CLEARLY could care less what anyone thinks of it. GOOD for her. Her moves are so sweet you almost don't even notice the excellent rendition of Elvis Costello's "Pump It Up" going on behind her.
I can't really explain what goes on around :51 seconds in. She's "pumping it up" perhaps?