Princess Stephanie does not wear a lot of jewelry. I have noticed that she does not pay a lot of attention to self-adornment. Maybe this explains her choices in simpler hairstyles.
A woman in her position could hire a personal hairstylist and spend a lot of time preparing for public appearances. But she doesn't do that. She has a spirited lively personality and it appears that she isn't the type to spend her time in the beauty parlor.
Maybe she has some of her Mother's practical DNA. Princess Grace could have worn extravagant jewelry like the jewelry that Elizabeth Taylor or the Duchess of Windsor wore but Grace did not do that. Grace had simpler tastes in clothing and jewelry. I think that in this respect, Stephanie is like her mother.
I remember what Prince Rainier once said about his wife. He said that Grace did not wast her time with personal masseurs, she didn't lay around and have spa treatments or covering herself in therapeutic mud, she was always busy. So it makes sense that since Grace's daughters were not raised with the example of a mother that set aside a lot of time for beauty treatments, massages and the like, that Stephanie has a tendency for simplicity and practical choices in clothing, hairstyles and jewelry.