Okay ... in CA. She took pictures of emails ... and, did what with them?
While it might be possible to pursue prosecution against the stepdaughter, it is exceedingly unlikely that any county in CA would do so given the limited info you've provided.
It might be better to secure the computer against further intrusion by NOT saving passwords, or, better yet, mandating a login and timing out.
PC 502(c)(2) is a wobbler punishable as a felony or a misdemeanor. But absent any real harm, and free access to the password, it is unlikely to result in prosecution. But, you can report it to the police and see what happens.
502(c)(2) Knowingly accesses and without permission takes, copies, or makes use of any data from a computer, computer system, or computer network, or takes or copies any supporting documentation, whether existing or residing internal or external to a computer, computer system, or computer network.