I prefer [name_u]Abby[/name_u] 
I knew an [name_f]Abigail[/name_f] in high school. Most people called her [name_f]Abigail[/name_f], she made sure only her close friends called her [name_u]Abby[/name_u]. This makes me think it’s not that inevitable. I also prefer the spelling ‘Abby’.