i'm scared of my mum travelling with my sisters on the motorway

my elderly mothers travelling to see my terminally ill aunt tomorrow, my sisters are driving her there, but they have to travel via motorway and motorways frighten me and i'm worried about my mother having to travel on one?

there's nothing i can do as my mum is going to see my aunt who is very ill with cancer and doesn't have very long to live.......my mum assured me that my sisters are good drivers, that my elder sister drives on the motorway all the time....but it still made me feel worried.