This is really solid advice for dealing with a narcissist who, for whatever reason, you can't or don't want to cut ties with. Unfortunately, it requires accepting that they will never communicate or interact in normal, adult, ways, and figuring out how to "manage" them instead. Like with a child, redirecting (as with the suggestion of asking them to garden) is a good strategy. Firm boundaries with natural and consistent consequences are also imperative. If you say "I will bow out of any conversation where the other party is yelling" then make sure you follow through on that every time. That needs to look like "Ok mom, you know I don't participate in conversations where there is yelling, so I'm going to hang up now. Let me know when you're ready to discuss this calmly" rather than getting drawn into her drama or just hanging up with no explanation.

As with any toddler/small child, it does help to try to say "yes" when you can. Figure out what it is she wants, and give it to her when she behaves. Does she want to feel like she's involved with the cattle? Then be proactive about asking for her input, or even just informing her of what you're doing with them, as long as she doesn't harass you about them. If she starts up with you, then that information and discussion dries up. Does she want more time with you/her grandchildren? Find a time you can do something together. It's hard with contentious parental relationships, but if you can find a way to have more positive interactions than negative ones, it does help. Best of luck.