Have a read here
http://scotland.shelt..._home/making_a_will#0
"Many people assume that when they die, their possessions, such as their home, furniture, jewellery and savings, will automatically go to their wife or husband, their partner or their children.
In fact this is not the case. If you die 'intestate', that is, without leaving a will, the law decides who gets your possessions, not you or your partner or family."
Your sister needs to see a solicitor.