1. I believe the guilty person to be her.

2. I believe the guilty person to be she.

3. The guilty person is believed to be she by me.

4. The guilty person is believed to be her by me.
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Which ones are correct? Do we have to use 'she' or 'her'?

The subject pronouns include I, he, she, you, it, we, and they. The second type of pronoun is an object pronoun, which takes the place of a noun that receives the action. Objects in sentences usually occur in the predicate of the sentence. The object pronouns include me, you, him, her, them, us, and it.