Is her a concrete or abstract noun?

The Word 'her' is not a noun. The Word 'her' is a pronoun.

The pronoun 'her' is a personal pronoun, a Word that takes the place of a singular noun (or name) of a female as the object of a verb or a preposition.

The pronoun 'her' is a possessive adjective, a Word placed before a noun to describe that noun as belonging to a singular noun antecedent for a female.

Examples:

Aunt Alice loves tulips. I think that I'll buy these for her. (personal pronoun)

My sister made the cookies. Baking is her hobby. (possessive adjective)