'dream of hers' vs 'dream of her'

[Handira]

English Language Tests, Intermediate level

ESL/EFL Test #275 "The holiday of a lifetime", question 2

This had been a dream of ......... since she was a child.

(a) hers
(b) she
(c) her
(d) she's

English Language Tests, Intermediate level

ESL/EFL Test #275 "The holiday of a lifetime", answer 2

This had been a dream of hers since she was a child.

Correct answer: (a) hers

Your answer was: incorrect
This had been a dream of her since she was a child.
_________________________

Please explain the sentence or define "hers"
why use hers?

Handira

[Torsten]

Hello Handira,

Please take a look at these phrases:

This is a friend of mine. (I have a many friend and this is one of them.)
This is a friend of yours. (You have many friends and this one of them.)
This is a friend of his. (He has many friends and this is one of them.)
This is a friend of hers. (She has many friends and this one of them.)
This is a friend of ours. (We have many friends and this is one of them.)
This is a friend of theirs. (They have many friends and this is one of them).

TOEIC listening, talks: Preparing an assessment of the museum facility