The Nexus — Kim Richardson

When Mrs. Dupont used Zoey to set The Great Junction in motion: the event that occurs when two portals from different worlds align and make a permanent doorway, with it came disaster. The two worlds cannot withstand the pull of The Great Junction, and now the worlds are collapsing.
What's worse, Zoey uncovers that her mother is kept prisoner in the Nexus. Together with her friends, Zoey must find a way to undo the damage, save her mother, and close the portals from both worlds before it's too late. Because if she doesn't, both worlds will end.