The narrator, a 16-year-old girl, is smart but still a bit naive. She knows a lot of things about fashion and famous actors. She knows what she should or should not do as a girl:

"Now don't get me wrong. I mean, I want you to understand from the beginning that I'm not really so dumβ. I know what a girl should do and what she shouldn't. I get around. I read. I listen to the radio."

However, her innocent heart still lets itself be deceived by a handsome and popular boy. She knows she is not dumβ, but she feels silly for waiting for the boy's call:

"I can sit here now and forever and laugh and laugh while the tears run salty in the corners of my mouth. For all of a sudden, I know, I know what the stars knew all the time - he will never, never call - never."

"Sixteen" is a short story by author Maureen Daly (1921-2006).
The narrator is a 16-year-old who begins by explaining to readers that she is not that dumβ.
That is already a sign of her insecurity. We can already foresee that something happened which made her feel dumβ.
It turns out that, although she is indeed smart, she fell for a boy who promised to call and never did.
Of course, that is normal and happens to anyone. But the narrator feels silly for having believed him. It's as if she feels less smart for trusting her heart.
In conclusion, we can describe her as being smart but naive. The narrator is definitely not a silly girl - she is just a human being who falls in love, like everyone else.