请问这是什么从句?While traveling in English,she met a friend of hers

请问这是什么从句?While traveling in English,she met a friend of hers Betty met a friend of (she,her ,hers)in the street. 请问,为什么是a friend of hers 而不是a friend of her? While I .【walk】 in the street ,I .【met】 an old friend of min while-----(walk) in the street,I met an old friend of mine填空 l met a friend of mine---- in the street yesterday She is writing a letter to a friend of hers,______ him to at Judy is a friend of (选择） A me B her C she D hers she is writing a letter to a friend of hers,____him to atten a friend of her还是a friend of hers Jane has just___ a letter from a friend of hers in England. While traveling on the Great Wall .we met with a few Germen