As a young girl, Reinette was innocent, gentle, full of curiosity and wonder. As a grown woman, she’s lovely, gracious, charming, but still as curious as ever, though now with a quick wit and sharp intellect to go with her other attributes.
The seemingly sudden transformation from child to woman, at least from the Doctor’s perspective, is unsettling although it probably shouldn’t be. It’s not the first time he’s met the same person at different stages of their lives, but the period between meetings is usually longer than a few minutes.
Time here has been accelerated. It’s really rather confounding.