"A shrewd girl who sells wares at high prices with the help of her father."

She and her father, who she passes off as sick (but really isn't), stands outside with him. When someone interacts with them, she'll beg them for money to help her sick dad. She'll give you an MP candy, the item that restores your MP mid-battle, in exchange for 500 gold. To put it in perspective, you can buy MP candy at the inn for 100 gold. If you say yes, the transaction will actually take place and you'll get stiffed out of 400 gold...all while she celebrates with her dad, who seems a lot better than he did a few moments ago. If you say no, she'll openly cry about it. I'd feel bad if her prices were a tad lower. 

For her voice, while she's trying to sell the candy, I'd imagine her to try and openly make herself sound more helpless; While she's celebrating, she should drop that act. The way I'd recommend you doing that is making your voice even higher-pitched. I want you to use a voice in the high range regardless, of course. Whenever she mentions her sick father, I imagine her putting special emphasis on that.