Her has two forms:
Possessive form of 'she': This is her pen; She is her mother
Object form of 'she': Give it to her; I know her
For simplicity, please let me refer to the first form of her as possessive she and the second form of she as object she.
The object she is surely a pronoun. But the case of possessive she is confusing.
The Longman Dictionary of Contemporary English says that possessive she is a determiner, whereas Swan's Practical English Usage says that possessive she is both a pronoun and a determiner.
I am confused. Is possessive she both a determiner and a pronoun? or is it only a determiner? If it it both, why does the LDCE define it only as a determiner?