I think it's one thing to make a complaint and vent about our spouses to someone we trust. It's another to do so chronically. Unfortunately, she is who she is and if she has anxieties about toxicity, you can't really change that about her.

I think it's ok to express that you're interested in knowing how her day has been, as long as she doesn't discuss your dad. It's fine if it's either neutral or positive. Maybe it's been habit forming.

Would she be interested in journaling? LOL I laugh because your mom sounds a lot like mine.. always complaining about her husband (and everyone else). I don't think mine would be interested in it at all. I should ask and see.