Maybe as her child gets older, you could gently and jokingly point out that yes, he was prem, but he can trash a toy box just as effectively as a full term, more robust child, and should therefore be expected to be just as clever at picking up?
That kind of thing. Gently put the emphasis on how similar your children are, and how they are both special, and not just hers.
But to be honest she sounds like a total princess about her life anyway, can you get her in an environment with other mums with even more horrendous stories/competative streaks?