。
She's friendly to everyone.
Literal
She [topic-は] anyone [to anyone-にでも] amiable.
誰にでも is the universal-quantifier mirror of 誰にも~ない — the same に target marker, but with でも ('even / any') replacing も to flip the polarity from 'no one' to 'everyone.' Used with affirmative predicates: 誰にでも優しい ('kind to anyone'), 誰にでも好かれる ('liked by everyone'). 愛想 (aiso, 'amiability, sociability') is the warmth and charm one projects to others; 愛想がいい paints someone as outwardly friendly and welcoming. Its counterpart 愛想がない describes someone curt or unfriendly — a quietly damning judgment in Japan, where social warmth is socially valued currency.