That's So Raven/WMG

Tanya Baxter has abandoned her family.
It's not that far-fetched. Victor is too embarrassed and hurt to admit that his wife left him, so her leaving to study law in England is just what he tells people. Who knows whether anyone In-Universe believes him.

Raven's visions are granted by a malevolent deity.
Raven's visions, most of the time, are actually about dumb pointless things. However, they're generally taken out of context and so Raven jumps to the worst conclusions. One example that stands out is when Raven has a vision of her father saying "we need to split up" to his wife. Raven assumes they're getting divorced, but Victor really just meant "Let's split up so we can find the ring I lost". Now, why would Raven have a vision of her father saying "Let's split up", causing her to jump to conclusions? Obviously there is a bored, malevolent deity who grants her these visions as a practical joke, so he can watch her act bizarrely trying to prevent visions of things she misread. As to why it appears to be genetic? Maybe the malevolent deity was betrayed by Raven's maternal ancestor and so he's exacting his revenge.
 * Could this bored, malevolent diety be perhaps a bored, malevolent writer?
 * Hello, Fanfic Fuel.

Raven is actually Raven.
And one of these days those rainbow swirls in her eyes will start to turn red...

Raven's ancestors from her mother's side are from the wizard world.
In "Don't Have a Cow," Raven and Chelsea find Raven's grandmother's old trunk, which had many supernatural things in it, including a book of potions, spells, and incantations. So, this doesn't seem too far-fetched.
 * Or, her ancestors were descended from a totally different Wizard-World, and a certain house became her namesake (Ravenclaw anyone?)

Raven has been a telepath as well as a clairvoyant all along.
In "Leave It To Diva," Raven endures what her mother calls a "psychic cold," which caused her to randomly hear the thoughts of those around her. Tanya states that her mother always had them, which is where this WMG comes into play. Viv could've been a telepath as well as a clairvoyant, since she was able to know everything about Cory's pranks. Raven, having inherited her grandmother's abilities, could've been a telepath as well, but never really developed, or became aware, of her ability. The "psychic cold" could've been an ailment where a telepath uncontrollably hears everyone's thoughts. Since in "Saving Psychic Raven," there were other kids who were both telepaths and clairvoyants, Raven could be one as well.