Firstly she started swimming around. That's not too weird. Nurse sharks can be pretty relaxed and hence very approachable when they're sat on the bottom as we've seen. They can also be quite shy and flee approaching divers. Saturday's girl did something quite different. She got up but then put on a bit of a threat display.
Although it looks like she's about to drop to the sand this is actually a classic shark threat display. Notice the arched back, dropped down/spread pectoral fins (the ones at the side of her head) and raised dorsal fins. This is combined with rapid turns back and forth and elaborate movements. Basically if you see a shark doing this, give it a little bit more room. Our little girl was no threat and I think she was just a little upset about 6 people who were bigger than her appearing in the middle of her nap. After circling a couple of times and giving the big display she swam slowly off to find a new place to chill.