Wicked Willow Series by Yvonne Navarro

Buffy and Xander arrive too late to stop Willow from taking revenge on Warren for the murder of Tara, and now they stand helpless as Willow determines to use whatever magick it takes to bring her lover back from the grave.

Even Willow's own coven has turned against her now. Condemned for saving Buffy from their evil phantom and for not protecting the other coven members fully, as she had promised, Willow must come up with a way to restore herself to them - and to reinforce her position of power, which hangs in the balance.

The Ghost of Tara has disappeared. At first Willow thought it was because of something she'd done -- or worse, that the universe was again conspiring to hurt her. But it's almost impossible to keep secrets from a witch, especially one as powerful as Willow, and ultimately she learns that Buffy and the gang are the culprits. Willow desperately wants Tara back. Not only does she miss her immensely, the spirit's presence is necessary to perform the resurrection spell Willow's been working on... moreThe Ghost of Tara has disappeared. At first Willow thought it was because of something she'd done -- or worse, that the universe was again conspiring to hurt her. But it's almost impossible to keep secrets from a witch, especially one as powerful as Willow, and ultimately she learns that Buffy and the gang are the culprits. Willow desperately wants Tara back. Not only does she miss her immensely, the spirit's presence is necessary to perform the resurrection spell Willow's been working on. Though her first impulse is to charge off and bring her wrath down upon the heads of her old friends, her coven reminds her that in the past, when Willow has allowed anger to control her, she has failed. Willow must develop an alternate plan to regain Tara's spirit and perform the spell. Buffy and the Scoobies hope to drain Willow's power, and release Spike and Oz from their enslavement. But Willow's anger is endless, and it seems she'll stop at nothing in her fight to bring Tara back, no matter what the cost.... less