Hello Lily, with having MI, anxiety and depression can certainly intertwine with each other, although on any day one could be stronger than the other and then reversed the next day, we don't know and we can't necessarily predict, not unless a situation we don't want to happen is going to occur against our will, then both or either one of these is more dominant.
When my ex had PND after our second child, fortunately, her mother was living with us in a family hotel who helped out an enormous amount as I was trying to run the hotel by myself, unfortunately, I also developed PND which I tried to hide and no one knew about it and never thought, back in those days, of getting any help, although my ex (now) had a couple of psychiatric sessions and then stopped ('81).
The most difficult task for anybody close to someone suffering from any potential mental illness is to be able to communicate with them in a dialogue they can understand and allow them to express themselves without interrupting or offering your own opinion which may cause them to close up, that's very difficult but certainly can be done in a tactful way.
If you are able to get them to see their doctor, that's a positive start where your help will be of great benefit.
Please get back to us.
Take care.
Geoff.