I can't tell if you're planning to take your MIL to a restaurant with a full bar, or plan to sit on bar stools for your meal. I just want to suggest that if you've never seen her sit on a stool for an extended period, don't make that part of your plan. Bar stools are not universally comfortable for all bodies (which is something that might not occur to folks who find them just fine. Seemed worth mentioning.)

I'm old enough to be a MIL and I love how well you seem to know her tastes and priorities for a good night out ... Have a great time!