My Wife did this to our Toyota Lucida about a year ago.
I got it home by the AA, then just siphoned off as much fuel from the tank as possible, drained the filter bowl, and refilled with Diesel.
It started OK after a few seconds cranking and ran fine after 2 or 3 minutes.
Did she drive it far after doing it?
If dhe drove it until it conked out, you may need to bleed off the lines up to the injectors as well.
A bit of petrol going through won't hurt it, it's worse putting Diesel in a petrol car.