Growing up Muslim I've dealt with some of the slick stuff people try to do to you when it comes to food.
I'm not accusing the school of intentionally feeding her daughter pork, but I have been in situations where I have accidentally eaten pork because people have failed to inform me there was pork in it ( even when I asked prior to eating ) and they knew damn well there was pork in it.
Yes you should inform your child of what to eat, she's a 2nd grader so she may not be sure of what is in every food.
When I was in the 4th and 5th grade, I had a lunch lady who was generous enough to let me if something had pork in it. But not every lunch lady is so generous.
However, I do think the mother should just send a packed lunch to school to be on the safe side. The mother should be glad her daughter attends a school where packed lunches are allowed because many schools nowadays do not allow lunch from home.