What are format are those fictions ? Manga ? Comics ? Book ?
For her appearance, just do a lot of concept arts really. Try different things while still having some references to the character you inspired yourself from. Heck, try to reference multiple characters if you want/can. But try to do something you like, don't bother yourself too much. Just find the perfect design for the character and you'll be okay. A character goes through a lot of designs before finding the perfect one.
As an example, Bugs Bunny took 50 years before having his official look that we know today.
Here's an other example...
Those were the very first concept arts for the characters of the first Ace Attorney game. The green attorney with a blu bowtie was originally going to be Phoenix Wright. It took a lot of time before having the official design that we all know today. Here's more images if you want to see how the character designs progressed, for Phoenix Wright and others :
So in short, don't worry about remaking desings and concept arts over and over to find the perfect fit for your character.