It depends on your mother's personality.
If she cares most about health give her Forks Over Knives or the Get Healthy Go Vegan cookbook - both written by doctors.
If health food is a joke to her, give her something with a catchy fun title like But I Could Never Go Vegan! or Veganize It! Easy DIY Recipes
If you think she actually cares about the ethical side, give her Alicia Silverstone's The Kind Diet or Vegan Planet.
If she is none of the above, but it very centered on ethnicity or culture - depending on your background, give her Mayim's Vegan Table if you're Jewish (I have a Jewish friend who is lacto-ovo veg and started making more vegan meals because of Mayim Bialik) or Afro-Vegan or Vegan Soul if you're African-American, or Vegan Mexico if you're Mexican ...you get the idea. If she's a conservative Christian give her The Biblical Cookbook: Meat which is actually an argument for Christian veganism. Trust me, even if you're white and she's Eurocentric, there's still The French Market Cookbook and Chloe's Italian Kitchen.
I hope this helps. I don't think there's one perfect cookbook to give your non-vegan mother. I think approach really should depend on what the individual vales and their personality.