a friend of hers的用法和样例：
- Mary was planning on seeing a friend of hers at the baseball game.
- She asked a friend of hers to dinner.
- A friend of hers gave the bride-to-be some condoms as a gag gift.
- He tricked the widow in the guise of a friend of her late husband.
- I would like you to meet a friend of mine.
- They were off to visit a friend of theirs.