Paganlass first congratulations on helping your Mum to get those bg levels down, you are both doing a really good job there, tell how old is your Mum?
Second, what a coincidence your post re mum with shivers is, only yesterday I spoke to 2 diabetics that I know one here in the UK and one over in Slovakia, both describes symptoms just like you did, and apparently this can happen as a result of extreme tension that can be brought on by various things including a sudden change in bg levels (that is according to both the UK and Slovakian doctors), when we are tense we contract our muscles, sometimes involuntarily even, and we might not even be aware of it ourselves, but this can make us shiver and we get more tense and just shiver and some even go into a kind of spasm with feeling so cold, and duvets, hot water bottles, heaters have very little effect on this, the person needs to relax, let go, relax the muscles, do some deep breathing exercises, like breathe in to the count of 3 and out to the count of 3 and think...w-a-r-m, 2, 3...sometimes a hot drinks, sipping it slowly helps relaxation too and the shivering stops.
So this might have been the case with your Mum? If at any stage you do become concerned please do seek medical advice, ring NHS direct or call your doctor.
I hope all goes well for you and Mum, big hugs to both of you.
All the best
Karen x