I have a great-aunt
Dorothy, whom we all call Aunt
Dot, or, on occasion, Aunt Dit-Dot, but I assume she was likely
Dottie (or
Dotty) as a child.
Dorothy is also my mom's middle name, but she doesn't like it.
If I used either, I would use
Dorothea with the nickname
Thea (or maybe
Dora, if
Dora the Explorer ever stops being popular). I think
Dottie is kind of cute, but
Dodie reminds me of Dodo birds, so would be a no-go for me.
For me,
Dorothy in particular still sounds very old-fashioned, but it's rising in popularity quite quickly and could end up being the next
Hazel or
Stella or
Ava.