Does anyone know the title of this children's book?!?

Question

I was younger when I read it. It's about a girl visiting...I think her grandmother. She got picked on and was given tea to make her invisible from bullies. It worked and then there was something to do with a crater she had to go to, which was a magical world, and she had this quest to save I think that world or just something, I believe. I can't remember anything else except that I was in 5th or 6th grade when I read it, I believe it had chapters, and I loved it! Please help! I've been searching for years and checked it out of a library in Ft. Drum, New York, where I don't live anymore.

Thank you Matthew S!!!!!!! You found it!!!!!

Answer 1

Perhaps it's The Ancient One, by T. A. Barron

Here's a website with an excerpt:
http://www.tabarron.com/tabarron/?cid=253,248,309,312,314

It was written in 1992 I think, so perhaps that's too late?
There's a similar story about magical tea that's set in Jamaica,
Dashalong something

Answer 2

This is a long shot, but was the author Madeleine L'Engle?
It sounds like something she might have written.

I hope you find it, it's always great to re-read something that you loved as a child.