I might be some help, but first I have some questions:
What edition are you running with? I need to know what ruleset we are dealing with. What kind of setting are you planning on playing with. Is it Ebberon, Faerun, Planescape, Dragonlance, Greyhawk, Dark Sun, Five Kingdoms, or Ravenloft? Or are you running some other setting, or a homebrew? The setting is extremely important. What type of magic do you want the character to specialize in, what kind of weapon do you want her to use, and what kind of backstory did the player already lay out for her? This is key information, as for example, if the player says she is from Calimport, this woman probably did not learn to be a conjurer at the Hosttower of the Arcane, and then learn to fight with a cutlass working as a mercenary escort for merchant ships in Waterdeep. If she raised the player's character in Daggerdale, she is likewise probably not going to have much in the way of occupation: sailor. What temperament does she have? If she is lawful good, she probably won't have taken any levels in rogue, and likewise, if she is chaotic neutral, she cannot have any levels in paladin. Once you clear this up, I would be glad to start working on it with you.