Are imaginary friends normal ?

About a week ago I was making dinner and my daughter was watching a show in the living room and I hear her laughing and then I hear her talking to someone I couldn’t quite hear what she was saying so I went to check on her and I asked who she was talking to she told me that she was talking to her friend (she was alone in the room) so got a little freaked out but I just assumed nothing of it and went back to making dinner well we were eating she asks if her friend Margo could sleep over when I asked who Margo she said my friend you met her in the living room I told her yes because I know Margos not real a little bit later I was giving her bath I left her for not even a minute to grab a towel and I hear her laughing so I stop at the door to listen and she’s having a full on conversation with herself she was saying stuff like how funny Margo is and that she’s her best friend I just assumed she will forget about it soon enough later I was tucking her in and she asked me to set up a bed for Margo I just played down a blanket and a pillow and left couple days later since then she mentions Margo pretty much everyday and it’s pretty much all she talks about

So I’m just wondering has anyone else’s kids had imaginary friends and when did it stop ?