Susan is okay, it has a pleasant sound but at this stage, on a little girl it seems almost like a placeholder name, like Mary or Janie. I think Suzanne is much prettier. Sue is a cute nn.
Frederica I don't like at all. It's heavy and hard and just ugly. There's a town here in Delaware with that name, though I think it's spelled a bit differently. It's pronounced something like Fredder-icka, with the second syllable very unemphasized.
"It's one thing to be open-minded and quite another to be so open-minded your brains fall out."--Dear Abby
"Let other people push you around, and you deserve whatever bad things happen after that."--Lauren Bacall