Mom likes to "piddle" all day. She is moving plants, decorations, stuff all day long. She puts things in impractical illogical places. It can make for lots of frustration. For her and I. She keeps everything. Too much excess. It's her house and I get that. She is active and I am grateful. I just want to make life easier for her and I.
What about doll houses with furniture - I remember how much fun we had when we were little, changing the dolls' clothing, rearranging the room furniture.
Lincoln logs were also fun; your mother could create with them. And they're probably much more sophisticated and diversified than they were decades ago.
I also like the idea of puzzles. Large piece puzzles for children would probably be easier to work with. There are also Chinese checkers and dominos, both of which could be played individually.
Some years ago I had an urge to focus on games we played while growing up, and after some searching, located some lovely marbles. I keep them is vases, sometimes as a base to hold artificial flower, occasionally changing the position and adding stones I've found while wandering or working in the garden. The patterns they create can be lovely, and peaceful.
I think working with yarn would be great; it would require concentration though, so it's a different level of attention. And sometimes older hands can't manipulate knitting or crochet needles.
Another thing you could do is ask for her help in organizing something, maybe old clothes to donate, something like that. She could feel she's working for a purpose, recycling to help provide clothing to people in need.
I do think it's good though that she keeps herself busy; to me that reflects an active mind, dementia notwithstanding.
Through the various stages, we have needed to change the environment to fit mom's needs.