She is a fake it till you make it. It's better to try to get back to being able to be happy than give in to depression. She does seem to be trying to fight it.
I believe she is swallowed up by Jim actually really leaving, as opposed to working on the rough patch, they had been together all their adult lives, they were (are?) Legally married. He just leaves and then it'st revealed he has a new woman, then he moves her in to his house and they pretend they're the happiest everrrrrr. Humiliating, hurtful and everyone knows so she has to put a brave face on. Little wonder she has had no appetite.
Unless she ate martha...
Her mate is there as much for her own sake in not wanting to be alone under lock down, it worked out well for both. Living with a depressed mate is tough work though.