Never heard of Canva but to do menus Word would suffice wouldnt it, or the free OpenOffice one that I can't remember now, Writer maybe ?GIMP is free but I found it tricky so your Mother in law may struggle.
Hope the word filter allows this...GIMPGNU Image Manipulation Program.Been around for a long time, supports layers etc.https://www.gimp.org/Suprised no one has mentioned it![edit] Apologies Red Raw did mention it.