T in Modesto, California said: My problem now...
Except it is not your problem. You have followed both legal and your own employer's rules regarding communicating such notices to your tenant. If she chooses to ignore them, then that's her problem, not yours.
You're in California. So legal delivery of notices to tenants includes posting such a notice on the main entrance to the rental unit. So long as you have documented yourself when you made such a posting and what it is, that's the end of your 'problem'; you have done your job.
So what if she sends you 'certified mail' (is it truly that or is she just labeling regular mail to that or ??) saying she didn't get it? You've done your job.
Since you can lawfully post such notices to her door, you're not being '(forced)' to mail her notices at all, much less certified. One of the reasons why posting is allowed is simply because some people will not accept certified mail. Posting notices to a front door obviate that issue.
You already have an attorney involved. So just do your job, which now is to simply deliver the notices by lawfully posting them on her door, keep a record of that (and signing/dating any such statements as required saying you did), and forward on any responses to the attorney.
BTW, there is no 'reasonable accommodation' when it comes to the lawful delivery of notices to tenants. That is just a bunch of bull. You can either hand it to her; post it onto the mail entrance to her dwelling; or certify mail it.... and that's it. It isn't up to her to decide which method she will or will not accept. That's your choice and that's it. 'Reasonable accommodation' has nothing to do with it.