In the Brothers Grimm version of this story, Little Snow-White, Snow-White is just as beautiful as her evil stepmother; however, unlike her stepmother, she is as beautiful on the inside as she is on the outside. Each day her stepmother asks her magic mirror who is the most beautiful of all, and every day the mirror answers:
You, my queen, are fairest of all.
Then she was satisfied, for she knew that the mirror spoke the truth.
Everything is good for seven years; at that age, Snow-White is "as beautiful as the light of day, even more beautiful than the queen herself." Unfortunately for the girl, other people have noticed her beauty, and one day the magic mirror speaks a new truth to the stepmother:
You, my queen, are fair; it is true.
But Snow-White is a thousand times fairer than you.
This evil woman sends her stepdaughter off into the woods with a hunter and heartlessly orders him to kill Snow-White. While the hunter has every intention of fulfilling this command, he cannot do it and tricks the woman into thinking he has done the deed.
Now Snow-White is on her own in the forest, and she is understandably frightened. What is interesting, though, is that while the wild animals she encounters as she runs lunge at her, they uncharacteristically "do her no harm." Just as it is about to get dark, Snow-White finds a neat little house and goes inside where she finds a table set with food and utensils for seven people. Because she is desperately hungry, she eats a bit from each place; then she goes to sleep on one of the tiny beds.
When the seven diminutive men return, they are upset that someone has been in their house, eating their food and, they soon discover, sleeping in one of their beds. When they see her, however, they change their minds; even more, they sacrifice their own comfort for hers.
They were so happy, that they did not wake her up, but let her continue to sleep there in the bed. The seventh dwarf had to sleep with his companions, one hour with each one, and then the night was done.
In the morning, she readily agrees to "keep house..., and cook, make beds, wash, sew, and knit, and keep everything clean and orderly" so she can stay here. The dwarfs warn her that her stepmother may still want to kill her, and they are right. The rest of the story is devoted to the stepmother's efforts to kill the girl and the dwarfs' efforts to prevent that from happening. Eventually a prince comes to her rescue and the stepmother is punished.
The Disney version of Snow White, of course, is older than seven, but she is quite similar to the Grimms' Snow-White. She is a a kindhearted innocent, unwilling to believe that people are capable of evil. Animals love her and she is protected by them as well as the dwarfs. She is both friend and mother to the dwarfs, and she is willing to work hard both to earn her keep and to makes the dwarfs' lives more comfortable. She is kind, perhaps even when she shouldn't be (as when she saves her stepmother who is disguised as an old hag), and she is optimistic. She has a pure heart and is a friend to all. In short, she is a true and noble princess.
Your question refers to her as having "noble character," and anyone who has that is bound to be a blessing to everyone she touches. Snow White and her stepmother both possess outward beauty; what separates Snow White from the evil woman is the beauty of her character and heart. These are the qualities that make her noble and make her someone others want to be near.