。
She should rest a little.
Literal
She [topic-は] a-little rest [should-べきです].
~べきだ (polite: ~べきです) expresses obligation or strong recommendation — 'should, ought to.' It's stronger than ~たほうがいい ('it would be better to') and implies the speaker feels the recommendation is objectively warranted. Here, the concern is for her wellbeing.