Is the word her a subject or an object pronoun?

The personal pronoun 'her' is an object pronoun.

The corresponding subjective, singular, personal pronoun is 'she'.

Example: Mom made the cake. She bakes a lot. I'll tell her that you liked it.

The pronoun 'her' is also a possessive adjective, a word placed before a noun to describe that noun. The possessive adjective 'her' can describe a subject or an object noun.

Example: Mom made the cake. Her cakes are very popular. She often donates her cakes to fundraisers.