Copyright law

My mother wrote a book, which was published by her 24 years ago. It was about her experiences as a nurse working in a hospital in Guernsey during the occupation of the islands by the Germans during the last war. 

She passed away about 15 years ago. In the leaf of the book it says that copyright belongs to her. 

The family would like to re publish the book (not for profit) but are being told that as she held the copyright and did not bequeath this to a family member at the time of her death we cannot reprint this book and publish it by law for 75 years after her death.