OK so I may have to move my mom to ALF - 'they' tell me dimensia patients may be better served by not having a private room? Any thoughts?

I'll agree with the others. It depends a lot on the roommate.

But overall, our LO has done cognitively better and is comparatively more content when she has a compatible roommate.

We asked her just to give it a try, and told her that if it didn't work out we'd arrange for a private room. It helps when they feel like they have options and choices.

Hi, flossie! ...I would have to agree with Bunnys_grl regarding the roommate. Last year my mom spent several months in a skilled nursing facility. Mom's first roommate drove mom up the wall. Their needs and personalities just didn't jive very well, and Mom wanted to have a room of her own so badly!

Later, her roommate left the facility (having completed her rehab), and THEN mom was LONELY--even for this woman who had been making her crazy. So we arranged a new roommate for her, and Mom and the new roomy became famous friends.

...so, most people do like company...but sometimes it really matters who that company is!

Flossie welcome in Glad you found your way here.
It is good to keep them stimulated but I would say it all depends on the room mate she gets.
Keep an eye on it, she may really enjoy the company.