The baby princess is only in the play for one scene, but Cranmer sure knows how to talk about her: "Those about her / from her shall read the perfect ways of honor" (5.4.44-45), he says—and yikes, that's a lot to handle for a little baby. You were probably wondering why this one little infant is so darn important.
We've got you covered, Shmoopsters: even though Elizabeth is a mere infant in the play, she grows up to be none other than Queen Elizabeth I. Elizabeth was on the throne when Shakespeare first began writing plays. Even though Henry VIII was written after she died, it was still important to give his former queen major props.
So when Cranmer (a figure representing the church or God) goes on and on about how Elizabeth will "be loved and feared" (5.4.37) and "her foes shake like a field of beaten corn," that's Shakespeare's way of saying how important this baby will be (5.4.38). It's his way of glossing over the fact that Henry really wanted a boy and was bummed when his baby daughter came along.
This way, Shakespeare focuses on how great Elizabeth will be (since the audience knows what's to come), rather than on how disappointed the king actually was at her actual birth.