As a driver, I must say that I cannot imagine Hillary would leave the line without the shoulder harnesses tightened. The belts are one of the most crucial factors in making a driver feel safe and comfortable when on the line. Many drivers, including myself, subscribe to the mantra "the tighter, the better" when it comes to safety harnesses. I would just feel "wrong" if I was on the line without being tightly strapped in.
Also, as a female driver, it's important to know that the shoulder straps are the most uncomfortable part of the harnesses. There is no way she wouldn't have noticed their absence. In my dragster, I know that I have to leave my right harness slightly looser than the left so that I can lean forward to reach the gears. Any driver would say something, or even shut off if their harnesses were not tightened. Especially one that just watch her mentor die doing exactly what she was doing. I'm sure it was a malfunction.
There wasa recent interview with a driver who stated they try very hard to do the exact same thing every time. From start up to shut off. To the point thats its automatic. Roll forward to the same spot, do burnout to the same point, back up, roll forward under the crew chiefs command , pull on the fuel pumps, set brake and everything in between, etc. I agree she would have prob. noticed the belts not being on. If someone messed up, it won't happen again, it just becomes a learning experiance, that luckily did not cause any one to get hurt, just shaken up.