if she is having trouble writing, then write for her. or if her voice is still strong have her tape her voice, without her image about how she would guide the family in the future were she able to still be around. as her teen daughters start dating what type of advice would she want them to have from their mom. As they move possibly into higher education and careers what would she say to her girls then. Also, as they girls head toward marriage (if that becomes relevant) the sorts of things she would want them to find in a husband ~ the attributes she can define through their dad as to what to look for in a mate. Talk about the joy of when they give birth (if they do) and how to cope with some of the stresses from pregnancy throughout raising little ones. are there favorite books they could read to their children that mom read to them growing up? keep them and be sure they get read to the next generation. how to cope with marital stress, how to stay grounded in a loving relationship and provide the example in your own relationship as to how that looks and functions. teach them how to fight fair as mature adults. teach them to be open to the changing fortunes of life ~ that adaptability is key. the importance of a strong foundation of ethics and morals. how much she loved her husband and the hope that they too will find love in their lifetime. tell them how mom views their personality traits and what roads she might think (in general mind you) they could pursue for their own development, whether a career or personal interest.
pictures are great and they are emotional memories but they tend to make us wonder what if she were around, what would she think about this... mom should teach ~ there is little that you can hold onto but once something is in the mind... "i remember mom said on that tape when i hit my 40's it was the toughest time with ailing parents and challenging children. what is happening to me is just normal, just like mom said it would be"
i would have her leave behind her life skills teaching legacy for her daughters ~ the biggest lesson of them all being death does not discriminate and life is so uncertain, take care of you and those you love. good luck to your family system and my sympathies for the difficult journey you embark on.