My mom with dementia has not had a BM for 3 days. Should I be concerned?

oh my goodness this is a familiar and on-going issue in our house. I would be concerned if her normal BM is more often. I would calendar every time my mom went and that's how we figured out she was becoming constipated. We finally started giving mom Citrucel every other morning and she's going more and it's not as hard as it used to be which is a big win. It does need to be drunk pretty quickly because it can turn thick but it's worked for us. It has that orange flavor so she doesn't mind drinking it. Best of Luck!

No three days between BMs is not anything to worry about. Think of how little elderly people eat, compared to a healthy fit 30 year old. The Citrucel or other brands of fiber drink usually help. Make sure the patient drinks a full glass of water after the ‘dose’. It can make a person clog up without enough water along with the fiber.

Add some orange squash to it to boost the orange flavour. Makes it taste soooo much better. :)
I take Macrogol 4 a day, every day. (I get it on repeat prescription, with my other stuff) 

 If you also have a 'drink of orange' at the same time, it will make it an enjoyable thing.  Trial an error what suits her, but there may be a blockage to clear first.

If she had piles too, this make it able to get past them. Be prepared for runny. But its OK, my doctors told me so.

I was is great pain from the constipation. I eat little but often. Suits me. That way I can digest it.

Good luck - hope you get it sorted soon.

From my experience, not at all anything to worry about...believe me when it comes, it comes in huge amounts so enjoy the poop free days. My mother is 95 and can no longer feel when she has to go so it tends to "leak" out when she has to go and it will be a couple of days of cleaning up and laundry until the next couple of days break. If it went on for a week, then you may want to call her health care provider and discuss it with them.