Legal Question in Business Law in California

This is probably not a question that can be answered in this online forum. It may be as simple as just walking in and operating the business. Most likely it will take quite a bit more. Contact a local business attorney. If your sister had an attorney she used, that would be the best person to contact.

My approach would be different. This is a matter that will be resolved under the laws of inheritance, i.e., the Probate Code. Who are your sister's heirs? Did she have a will or trust, or pass away intestate? The business will now belong either to whom her will or trust specifies, or, if she had none, its ownership will be determined by a set of laws governing "intestate succession." While the attorney that set up and/or handled the business might have some knowledge and competency in this area, I think you are better off going to a lawyer who specializes in wills, trusts and estates. If your sister had other relatives or friends, maybe someone has already started the process of getting her affairs before a judge in the probate court. Also, the business may be floundering with nobody managing it, so act fast -- but don't assume you now own the business. That may be the end result, but there are legal steps to be taken.