I read a series of 6 or 7 books about 15 years ago. I need help remembering the name of the series, I don't remember the name of the books or characters. I only remember the plot line and a couple of odd things that happened. I remember a girl travelled to another world or time at first by accident with a machine a teacher? She helped made. It was at his home where she would go after school. I remember she became a good archer and while she was gone for 6 months into this other world, only a few hours or a day or so would pass in our world.

There are a lot of books about kids time traveling. You could check Time City and I'd also review Chronicles of Narnia, because the way time works sounds very similar to that series. Try to dig up a few more details if you want a more specific answer.