。
I hear she's a skiing expert.
Literal
She [topic-は] skiing [genitive-の] expert is [hearsay-そうだ].
専門家 ('expert / specialist') is a productive compound: 専門 ('specialty / field of expertise') + 家 ('practitioner / person of'). The 家 suffix turns a domain into a person who works in it: 音楽家 ('musician'), 政治家 ('politician'), 芸術家 ('artist'). The hearsay ~そうだ at the end attaches to the noun + だ stem and signals 'I hear that...' rather than direct knowledge — the speaker is reporting second-hand information.