Unfortunately I have no helpful advice for living with someone with PPD. Typically what people believe is 'trying and supportive' ends up looking a lot like compromising themselves rather than compromising. Accept that you may not be able to do much for her, if anything, and try to maintain your boundaries and not lose yourself.

By not losing yourself, I mean, her paranoia and fears are not your responsibility. In a healthy relationship we are mostly responsible for our own feelings. I say mostly because, for instance, we may come to ask or depend on our partner to esteem us from time to time and the relationship can still be healthy. However, there is a difference between a request for emotional support and an obligatory responsibility. If she was to demand proof that you were at the library, are you able to say 'no'? It is not your responsibility to assuage her paranoia at every turn and if you accept that responsibility then you are not helping her, you are enabling her.