Have to play Devil's advocate here....
If it's food poisioning, it may have been from a meal eaten up to 72 hours BEFORE the onset of symptoms. So, if the McDs was the last thing she ate that may NOT have been what actually made her sick.
I got samonella from Bojangles chicken. It took 2.5 days to get sick from it. The reason I know for SURE that is what it was is that my hubby and MIL all got sick within 2-3 hours of each other, and the last meal we all ate together had been the Bojangles 2 evenings before.
Funny thing is, the last meal I ate before I actually started showing symptoms was Burger King. It was YEARS before I could go back to Burger King, even though I knew that wasn't what made me sick. Was eating Bojangles again before the BK...