the girl next door
US /ðə ˌɡɜːrl nekst ˈdɔːr/
UK /ðə ˌɡɜːrl nekst ˈdɔːr/

1.
a very ordinary, conventional, and wholesome girl or young woman, especially one who is considered attractive but not glamorous
:
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She's always been the girl next door, friendly and approachable.
•
Despite her fame, she still has that innocent girl next door charm.