What would her breast size be?

If a girl is around 14 or 15 and has a bra size of only 32a, but her mom is a 36b and the rest of her family are a and b cups; but her dad's side of the family all have DDs, would she stick with her mom's genes because of her current bra size, or could she be likely to fall in the middle when she's done growing?
What would her breast size be?
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