What's this anime?

It was an anime series that I remember first finding at Video Warehouse rental stores both near me and in NYC around 1998-1999.

the protagonist was, i believe, a girl with i think a female ghost acting as an alternate personality. they would swap when a fight was needed and would eventually turn back. it was set in modern era Japan. The anime was dubbed but I can't remember the name nor any character names whatsoever.

sorry for it being such a vague explanation but I would love for my wife to watch this as I think it'd be a great show for her.

I tried googling into it but seriously nothing popped up. Anything else you remember?

Yu-Gi-Oh, protagonist looks like a girl and can't even win a card game without swapping with his alterego.

Just kidding, quite sure it isn't Yu-Gi-Oh you're talking about.

The swapping in fights? Is it a bit like in Shaman King?

I honestly can't remember much more about the anime other than maybe the protagonist being blonde or brunette hair and middle school/high school age. unfortunately anime characters look in their 20s at times and are supposed to be like 13 :P