I don’t know what it is with me and mismatchy nicknames today. Anyway – thoughts?
I’m pretty liberal when it comes to nicknames, but I can’t see [name]Abby[/name] for [name]Annabel[/name]. (I’ll keep trying, though.) 
I can see [name]Anna[/name], [name]Annie[/name], and [name]Belle[/name] as nicknames, but I’m not feeling [name]Abby[/name], mostly because [name]Abby[/name] feels trendy to me compared to [name]Annabel[/name].
I don’t mind unrelated nicknames, though, so if you’d like to call her [name]Abby[/name], I don’t see any harm in it.
Good luck!
Similar to your [name]Josephine[/name] nn [name]Sophie[/name] question, I think it would cause confusion as they are separate, unrelated names. But that’s just my opinion. I quite like [name]Annabel[/name] and wish [name]Abigail[/name] weren’t so popular because I think it’s lovely, and [name]Abby[/name] makes it more youthful to me.
Thanksd for the opinions!