Very young infants are incapable of "manipulation". You have to have a sense of self before you seperate your"self" from the entity that is your caretaker. Until a child figures this out, all crying is need based only.

Now, a child of a year and some months, could be learning this, but maybe not as well. I would say that Moms should listen to the cry. Fearful cries are very different than tantrum cries, or completely fake ones (and when a kid is crying simply to manipulate, it is fake).

Tell your friend to listen to her Mommy instincts. That's what we have them for. :D