She is beautiful. She’s just not an Ancient Greek.
Homer described her thus:
“White-armed Helen” (λευκώλενος Ἑλένη) — white skin, untouched by Sun, softness, aristocratic beauty
“Fair-haired” / “beautiful-haired” — implies light or shining hair
“Helen like the goddesses” — her beauty is repeatedly compared to that of immortals
“Lovely-cheeked” — a conventional Homeric marker of female beauty
Euripedes was more explicit:
Fair hair, glossy, flowing, and long
Whitest of skin