So honestly?.... this post IS on the back of (and inspired by) a 'Thea' being called 'Teddy', which I really do LOVE, so that probs makes this a TAAT ( anyone?).
But in the spirit of the former, I know a lovely lady with a beautiful girl called Leontine. I'd never heard the name before but it is a 'known' name (https://nameberry.com/babyname/Leontine). For her nickname, the tot is called Leon, which I think is lovely for a girlie in much the same way as Teddy is .
My DD is named Andie but it isn't short for anything. It's Andie with Rosa as a middle. We always get people saying how much she suits it but we obviously also get people judging it and what it will look like in the future on her CV ect, it really doesn't bother us as I believe if she has the qualifications and the ambition she'll do well regardless.
I know a Frankie (Francesca) who was known by that name when we met at school and still goes by that name now, even professionally. I also know a Phil (Philippa) who is only Phil to people who are more than acquaintances and is Philippa professionally.
I am not sure what their parents think about it, although I do remember Frankie always being called by her full name by her mum when I visited.
To me, abbreviating Lorelai to Rory makes no sense. I don't get it....
But I do like the Harriet/Hari, Theodora/Teddy (or Theo!), Francesca/Frankie thing. Loads of other good examples too. It works because either a) the girl in question is a tomboy and likes it, or b) the girl in question is sufficiently girly that the boyish nickname still doesn't make them seem manly!