Is the pronoun in the sentence reflexive intensive both or neither Joan helped herself to more pie.?

In the example sentence, the pronoun 'herself' is a reflexive pronoun. The pronoun 'herself' is simply referring (reflecting) back to the antecedent 'Joan'.

The reflexive pronouns can act as intensive pronouns when used to emphasize its antecedent; for example: Joan herselfmade the pie.