I have been trying to remember the title of a book I read when I was younger.

All I can remember about this, was that it was a series (3 books total), it was about dimensions, I believe the main character was female, with a silver/white haired boy that was from another dimension. I only remember the name of one of the characters, the name is GiGi.

I want to say this book is mid 80's - 90's.

Any help would be great!!

You're not thinking of Madeleine L'Engle's A Wrinkle in Time, are you? I don't recall a character named GiGi, but it is the first of a series of books about a girl and multiple dimensions.