Legal Question in Wills and Trusts in California

Property received by gift or inheritance is not community property unless given to the two of them AS community property.

Additionally, if they are living separate and apart their own income would generally not be community property.

In other words, it's unlikely that he would have any rights to receive any of her inheritance.

An inheritance is separate property even if you are happily married and living together, so unless your sister converts her inheritance into community property she will be fine. Since they have been apart for many years and filing separate taxes she probably already has all of her own bank accounts, but just a reminder that she whould put her inheritance into an account that is in her name only and that has never been a community property account.