What type of Nobility are you using? Medieval, Oriental, Tribal?
Regardless of style, the important thing to note about being Nobility is that he/she is part of a Noble family. Without havng the family statted out (or at least in name and rank only), she may not know where she stands along the totem pole. Just "being Noble" isn't enough; you need to know HOW "Noble" you are.
My suggestion is to create a small family tree, and find her place in it. Make up some relationships between the family members, or at least find out how she perceives some of her family members.
Next, Nobles generally only hang out with Nobility. Hence, she may not want to be seen hanging out with commoners, nor doing any physical labour (that's what serfs are for). In short, just role-play her as a celebrity with lots of money and nothing but time on her hands.
With no work to occupy her day, she may be free to explore her own interests, or perhaps she is an active member in Court. Maybe she's a diplomat between her kingdom and others; maybe she's a fop and does nothing all day but eat, sleep, and compose poetry. Or, perhaps she disguises herself to hang out with commoners (a common theme, I know, but one that works). Perhaps she has a desire to rule, and strikes out on her own, or maybe she could be assigned a small garrison to man and keep the peasants in check. Or maybe she's like Zorro, championing the common man and bringing criminals to justice.
I hope this helps, or at least gets the creative juices going.