California has both a Right of Publicity statute and recognizes a common law right to one's own name and likeness.
The statute, California Civil Code Section 33.44, protects a person's right to control how his/her name, image, voice and signature are used for commercial purposes. Damages that can be awarded a person, when any aspect of their persona has been used for a commercial purpose without permission, include any actual damages suffered, any profits realized by the unauthorized user, and potentially punitive damages.
Actual damages can include not only economic losses but "injury to peace, happiness and feelings." (Tom Waits v Frito-Lay, Inc, 978 F.2d 1093, 9th Circ, 1992 )
That said, swalsh is probably right about there not being a lawsuit lottery here and he is right about the first step you should take.
If upon your request the website will not remove your wife's picture from their home page (and if there is nothing in the TOS that gives them rights in all content posted on the site), then you could speak with an attorney in your area and have the attorney send a letter to the website advising the site that the picture of your wife violates her right to publicity and should be removed immediately or legal action may be pursued.
The costs involved in pursuing a legal action, as a note, could very easily exceed any damages that might be awarded should you win a suit (and I am not sure you would win. . . .a personal review of the site and the facts is needed to determine this for sure).
Good luck.