Did my friend get ripped off?

Hi, my elderly friend recently had an oil change. A week later she finds her vehicle with a puddle of oil 10 feet long and 1 foot wide underneath her car in her parking garage. Her mechanic, same place who did the oil change said her crankshaft seal had blown. My boyfriend who knows a lot about engines said this would not cause such a large leak in a parked car, overnight. They charged her $450. Boyfriend believes they didn't tighten the oil cap and it became loose allowing all the oil to drain out. She's on a fixed income and this money is causing her distress, so if we can find out, they were just covering their assets) and made up a story to explain, we could possibly get her money back. Any help would be much appreciated, thanks so much. Colleen in Canada