not haveThis is part of a verb phrase with ter in the subjunctive or another form, followed by the reflexive pronoun se and a past participle: não tenha se assustado means “hasn't gotten scared” or “didn't get scared.” The exact English translation depends on the verb that follows.
PO: Espero que ela não tenha se esquecido do compromisso.
EN: I hope she hasn't forgotten about the appointment.