The future tense is not ordinarily used with adverbial phrases like "when she grows up." Instead use the simple present.
When the building is finished, it will be the tallest in the city.
The whole family will be there when we sit down to eat this evening.
He will be taught how to drive when he is older.
Because these describe future events there is a certain amount of speculation. For example, I don't know if the building will be finished. I'm just making a claim about when that time comes. The future tense conveys this nuance of possibility, as does other structures like "should", "can", "could", "would", and so on.
The simple present tense, however, conveys certainty. You would not use the simple present to describe future events unless somehow you knew them to be true. So when you say:
She grows up to be beautiful.
you are predicting the future, like an oracle.
Either that, or you are telling a story about events that happened in the past, but for some reason choose to use the present tense.
In the fairy tale of Snow White, which takes place long ago, a princess is born in some faraway kingdom. She grows up to be very beautiful, so much so that her evil stepmother, the Queen (who until then had been considered the most beautiful woman in the kingdom), is insanely jealous.
This is not common, as most stories are told in the past tense.