。
She can hardly relax when she's around people she doesn't know.
Literal
She [topic-は] not-knowing person [with-と] together [genitive-の] time [topic-は] almost cannot-relax.
Two grammar points to notice. 知らない人 ('person whom one doesn't know') is a relative clause modifying 人 — Japanese builds these by simply placing a verb-final clause directly in front of the noun, no relative pronoun needed. ほとんど~ない is the standard 'hardly / barely / scarcely' pattern, where ほとんど ('almost') paired with a negative gives 'almost not.' くつろげない is the potential negative of くつろぐ ('to relax'), so the literal sense is 'cannot relax.'