You'll probably find she'll just find her own groove with her name anyway.
I'm a teacher and often have kids with the same name - some get called Name then initial, some get shortened and some get their entire first name and last name.
I once had a child who asked us to call her by her shortened nickname (I always asked the kids what their preferred name is - even kids without the same name like their names to be shortened). That's generally what we go by. This girl's mum got upset and told her we had to call her by her full name (which was fine) except the girl herself really didn't want it. It was tricky. But we worked it out. I felt sorry for the poor little girl - her name was quite long and she looked so disappointed when her mum forced the issue.