。
She is a very pleasant neighbor.
Literal
She [topic-は] very amiable neighbor is.
愛想のよい is the relative-clause form of 愛想がいい ('amiable, friendly, sociable') — note the が→の swap that's standard inside relative clauses modifying a noun. 愛想 itself describes the warmth or charm someone projects toward others; its negative form 愛想がない ('cold, unwelcoming') is equally common. In neighbor relations, 愛想 is the small daily currency that keeps things smooth.