The Wizard's Dilemma — Diane Duane

How do you fix what can't be fixed? Only the Transcendent Pig knows, and it's not telling.... But Nita Callahan needs to find out, and soon, because there are important things in her life that are broken.

Her wizardly partnership with her best friend, Kit, has fallen apart. Much worse, her mother has gotten sick ... so sick that she may never be able to leave the hospital. At least, not without a little magical intervention.

Nita could use some wizardly assistance, but only One person can help -- the One she's devoted her life to fighting.