If your mother was in a private nursing home and funded privately then Govenrment regulations etc. don't come into it. In any case I think they only allow for a very small amount of pension to be kept - for use on minor essentials.
It should be possible to find out how much the house was sold for (less any mortgage and selling costs) and how much the home fees were. You would then know whether you have been conned out of some of the proceeds of the house as well as the rest of the estate. You certainly need to take action, but suing her could well be difficult and expensive if she is abroad. Of course, you have to find her first.