I'm pretty damn proud of my parents naming! If only they'd had the kids and didn't feel the need to cram all the names into mine (
Claire Georgia Wilhelmina "
Georgia"). Way too much!
I recknon that as long as you wouldn't call the kid
Abby as well then that would be totally OK.
Abby and
Abigail don't sound too similar when separated like that. Plus, depending on how old
Abby is now and when you have a daughter, you could name her after her? Especially if she's an important part of your life. Depends on how you feel on honouring names I suppose.