Having a new baby is highly stressful... she has every right to go out to dinner... and seriously - a nursing baby is usually getting used to a routine of feeding. If you are out, and the moms body says, OK.. its time, she really has no choice other than to nurse her baby. She shouldn't have to go sit in her car or some other place to do something that is a natural act...

And as others have pointed out, she was trying to keep it covered up...