、。
She's a popular musician, but very modest.
Literal
She [topic-は] popularity-having musician is [but-が], very modest.
The expression 人気のある ('popular,' literally 'having popularity') uses a relative-clause structure with ある to modify 音楽家. The adjective つつましい (慎ましい) means 'modest, reserved, humble' — it describes a quiet, unassuming nature rather than modesty about specific achievements. The clause-final が connects two contrasting descriptions — she has fame, but doesn't act like it. This contrastive が is slightly more formal than けど.