My 14yr nice may have multiple personalily. How do i fine out ?

You take her to the doctor and tell him what has been going on and they will do test

If she pretends she is someone else and she actually believes it herself, than she has multiple personality and there are medications that could help her with that.

I DONT THINK SO, 14 year is too yound to believe and think of MPD , but may be she behave differntly, mostly youngsters in this age does like that, she need littel more space , more freedom to express her self and may be join any older kid activity, its normal for 14 year boys or girls, just pay attention to her, chit chats, let realise she is grown and make her own decisons under the elders.