I agree with your sense that something bigger might be going on. Breast fed babes never have trouble pooping...in fact it's formula that makes them "stuffed up." Are you sure that you're friend isn't supplementing? That often happens when a new mom's confidence gets shaken, and she worries that she's doing something wrong.
Otherwise, if she is nursing is exclusively, I would encourage her constantly and also remind her that she would also want to be careful about eating onions, coffee, chocolate, and garlic as well as broccoli...gas producing foods that aren't easy on the digestive tract. Those can create so much gas that a poo would be painful because of the gas and tummy upset. I'd remind her to stick with foods along the lines of farm cookin,' if that makes sense. Chicken, noodles, rice, fresh veggies, salad, potatoes, fruit. If that doesn't help in about a day or two, then baby might have an allergy? Other intestinal issues? Has she tried a few drops of Mylicon in a bottle of pumped breast milk?
I definitely agree that the advice from the pediatrician about waiting it out doesn't seem quite right if you've seen first hand what kind of pain he's in. Always go with your intuitive feeling that something feels wrong and don't question your instinct to act on that, because no one will advocate for that little baby like his mom and her friends.