The correct usage is “she and I”, not “her and I”.
“She and I” should be used when the two pronouns are serving as the subject of the sentence. For example:
“She and I are going to the store.”
This is because both “she” and “I” are subject pronouns.
“Her and I” is incorrect because “I” is a subject pronoun while “her” is an object pronoun. You cannot mix subject and object pronouns like that.
Some references that support this:
- This Quora answer clearly states that “She and I” is correct because both are subject pronouns, while “her” is an object pronoun.
- GrammarCheck.me also confirms that “she and I” is the proper grammar when both pronouns are serving as the subject of the sentence.
So in summary, when using two personal pronouns together as the subject, it should be “she and I”, not “her and I”.