Then she's lonely and embittered.
So since this isn't a new thing, the only new thing going on is that you're tired of it.
This is your mother, not the debate club. Your interactions by definition will be different with her.
Everyone on the planet has someone they have trouble having a civil conversation with, but they have to deal with that person. Consider whatever triggers you and gets you pissed off when you talk to her, and keep those topics off-limits. And, as I said before, give yourself an out and somewhere to be, so this crap doesn't drag on and on. Become good at changing the subject.
Practice these helpful sentences:
- That's fascinating. Please pass the peas.
- I really don't think it's fair to discuss Elmer's weight when he's not here to defend himself. Did you hear he got a new cat? (adjust accordingly whenever a topic you want to be off-limits is brought up)
- Hasn't the weather been spectacular/awful/unpredictable? Have you seen the autumn leaves/new shoots on the trees/snow/neighbor's prize petunias/chipmunks? (adjust accordingly but talk about the weather and nature, pretty safe subjects most of the time)
- I just started taking a yoga/scuba diving/pottery/painting/English class and I'm having a lot of fun with it (adjust accordingly; also useful when you need to make a quick getaway, as you have to practice or study or classes are about to start or you need to pick up supplies, etc.)
- Gee, that apple pie looks great, but I promised Margie I'd clean her gutters and it looks like I'm late already. Maybe next time, and thank you. It does look scrumptious (adjust accordingly, but the concept is you are able to ditch but without hurting her feelings, particularly if she put some effort into something or other)
Of course you can figure similar things out on your own.
But remember two things:
1) You don't have to talk about anything you don't want to, so don't bring up unpleasant stuff. But the corollary to this is, you have to talk about something, so be prepared with some subject matter and
2) You don't have to be held captive forever. Put a time limit on visits and enforce it. The corollary to this is, in particular if you are called at the most inopportune times, start initiating the phone calls and visits and take back your own schedule.