Spite is bad
Willow knew that spite was not a good thing. Especially not spite against someone you loved. Besides having all the psychology books the daughter of a psychologist could want, she also had Xander’s family to look at.
She was going to go a week without magic, show Tara she was not to dependent on it, and more than that she was going to show that Tara didn’t get to judge her and decide that she was doing to much magic, just because they were in a relationship. After all, Willow wasn’t telling Tara she wasn’t doing enough magic, which frankly she wasn’t. Tara had barely upgraded her offensive spells while Buffy had been dead, and they’d only worked together on magic a handful of times since Willow had fixed her mind.
So, seven days... wait, she’d volunteered a month. Darn it. Of course Tara hadn’t taken her up on that. Oh, well, she’d do eight or nine days then clarify things.