。
She's a girl who looks cute.
Literal
[topic-は] in-appearance cute girl [copula-だ].
みための (or 見た目に) literally 'in-appearance' is an adverbial phrase modifying かわいい ('cute') — limiting the cuteness specifically to visual appearance, as opposed to personality, behavior, or other dimensions. The implication can be subtly mixed: 'cute to look at' invites the reader to wonder about the rest. かわいい is one of the most culturally loaded words in modern Japanese — its meanings span from 'cute' to 'lovable' to 'pitiable' depending on context. The whole word has spawned an entire aesthetic and global cultural export (kawaii culture).