First of all, I cannot give you any legal advice. I can only share my own experience with the issues you mentioned. Your sister might want to consult an attorney to get the answers she needs.
I live in WA and we also have the community property law here. It makes dealing with the financial side of being married to a cg pretty difficult on top of everything else. There are some things your sis can do to protect herself and the kids right now. She can sign up for a good credit monitoring service for herself and her hb as well. Can be done online and she should not share the password with her hb. Personally, I did not share the fact itself with my hb. She might also pull the credit records from all three agencies for both of them to see if there is anything he did not tell her. I got a post office box with only one key so I could check all incoming mail. That was very helpful. If the bank accounts are in her name only, she might want to have the bank put a red flag on the accounts in case her hb tries to go behind her back. No need to be embarrassed, my bank actually told me that I was by far not the only one with the alerts in place. If she does online banking, change the passwords frequently and not share them with anyone. If the car(s) is/are in both names, change the title to her only. My hb sold both of our cars behind my back. It is very important that she keeps cash and bank cards in a safe place at all times. Cgs are very sneaky and smart when it comes to finding resources for money. Last but not least she might want to make sure that the taxes are filed correctly. I left that to my hb and surprise, it resulted in a huge debt which left me no choice but to file separately ever after.
California has a Council on Problem Gambling and Gambling Addiction. It is located in Anaheim and you can find the website online. These councils are present in almost every state and are a great resource for info of all kinds.
Hope this helps a bit.
As an afterthought, your sister is very lucky to have you as someone to go to for help and support! It is so very important to not fight the battle alone.
