Legal Question in Criminal Law in California

If you want to challenge the validity of the will, you must do so in probate court. That is not a criminal forum.

Your sister could only be charged with murder if her actions caused your mother's death and if there is probable cause to believe she intended to at least cause your mother great bodily harm. Your question does not suggest that either of these things is true.

It's not clear to me offhand whether your sister's actions -- assuming she did what you say she did -- would amount to criminal elder abuse. Such charges require physical, emotional or financial harm to the elder, coupled with the intent to cause such harm. Altering your mother's will harmed you, but it didn't harm her. Overmedicating your mother could qualify as physical harm, but it would take a lot of Darvocet to do that. What's more, it could be difficult to prove that your sister intended to harm her rather than to ease her pain. Evidence that your sister altered the will after drugging your mother would be very helpful in proving such intent.

If you think there is proof of your accusations, contact your local police or prosecutor.

Good luck.