Maybe I'm dense or hard of hearing, but I never heard exactly on what basis the box was deemed to be "unclaimed". Did she fail to pay the rent for 3 years? If so, did she receive a bill during those 3 years and just not pay it?
When I switched states, I did have some problems with getting certain things forwarded to me in the mail. In fact, the more important, the less likely it was to be forwarded. For instance, my accountant asked me why I hadn't submitted a 1099 for a bank account that I had used for several years. Turns out the bank "lost" me. No problem getting another 1099, but this is one time I'm glad I used an accountant for my taxes. Frankly, I forgot about this account (which I had closed out, but did receive some interest during the tax year).
So, I guess I can see how easy it is to "lose" someone, but I know for a fact it's also easy to "find" someone if you really want to. The banks should do it, even if the CA tax folks won't. Maybe since it cost them a settlement, they will be more inclined to find folks in the future - but I wouldn't count on it!