My stepdaughter (18) 'imagines' I get into her room!!!!! Is it an excuse?

She is giving excuses that she wants a lock on her door, reason? She says someone gets into her room while she is away. I am the only one in the house during the day. My children (14 n 6) come back to the house in the evening. Honestly, I have never got into her room or allowed my children in her room. We had a talk me and her dad and I was visibly annoyed. I asked my children if they have been to her room, they said they have no interest in her things and were also annoyed by the allegation, I told them to keep off her room and I make sure the door is closed. My stepdaughter has not been happy that we lock our door, Im suspecting she also wants to lock her door and she is looking for excuse. Im the adult and I dont want to act stupid. Because of my faith n my age I feel like I should not revenge. If u were in my shoes, what would you do?