Magic for a Price by Devon Monk

 So, the wells of magic in Portland are poisoned, the city is surrounded by hostile magic users, and the most powerful set of soul complements is in charge of the world magic authority, and wants to destroy or enslave Allie and her friends. Time to rock n roll, eh?

Allie, Zayvion, Terric and Shamus are barely recovered from the last battle, but it's time for them to step up and take on the coming wave of attackers. A conclave of all the concerned parties; magic users, the police and the Hounds, is called, and Zayvion nominates Allie to take charge. She decides that the first and most important thing to do is to clean the contamination from the magic wells, then to delay or stop the incursion of the Seattle magic users who are on their way, and finally to somehow or other defeat Leander and Isabelle.

Allie consults with her father's spirit, which is still possessing her at times, and he tells here that he believes that by filtering the magic through Stone, the gargoyle/magical construct, and then seeding the wells with the result, they can be cleansed. The wells have been sealed for a while now, and must be opened to cleanse them, as well as re-sealed so that the invading magic users can't tap them to attack with, so Allie decides that she and her three friends, with the addition of Dr. Collins, can get the job done, and they head off for the each of the wells, in succession.

I think this is the final book in this series, as things go more or less according to  Allie's plan, though not without pain and struggle along the way. Allie's dad's spirit is finally removed from her body, and she learns about most of the details of her missing past. Magic is clean once more, evil is destroyed, and most of the good guys survive the battles. And, by the way, the moral of this story, like so many others these days, is that you can't go it alone, you have to trust and love your friends.