group of girls travel through a portal with individual paperweight things that act like keys

Question

It is about a group of girls who live in a neighborhood with a garden in the middle. There is a little building in the middle of the garden where they like to meet up. One day they all get these little triangle (pizza shaped) pieces mailed anonymously to them. When they put it on the table in their building, all the pieces slide together like magnets and open up a portal on the table. Some girl with green hair pops out and calls them princesses and says they need to save her world. They all agree and go through the portal. There are other details that I remember

• each girl's "key" has something to do with her powers. Allie has a plant and she can see life glow, her sister has a bear, some girl has a serpent, another one has a book and she can do magic, one girl has a unicorn and etc.
• one girl accidentally made a tornado by trying to cast a spell
• one girl can turn into a mermaid/serpent thing in water
• they meet village people who give them little clay beads or whatever
• spiders are bad
• there is a water or glass or ice unicorn which is the "source of all magic
• there are big bears which take them through the forest and one girl can talk to them. this is so frustrating I remember all this but I have no idea what the name of the book is or who wrote it!!!

Answer 1

I think this is probably Wellspring of Magic by Jan Fields.

I cannot find a copy of the book to confirm this is the book you describe, but one of the reviews gives the description:

Six eleven-year-old girls of diverse backgrounds and interests move to the same town at roughly the same time and become friends. One day they each receive a mysterious little metal triangle engraved with an image, a different image for each girl. When put together, the pieces form a gateway into a Fantasy World Mark 1 (dragons, magical guardians, and native fairy folk edition). In this world, the six girls turn out to be princesses who are sent on a quest to restore magic to the land.