Formal:
* She has blonde hair.
* Her hair is blonde.
* She possesses blonde hair.
Informal:
* She's got blonde hair.
* Her hair is blond. (American English)
* She's a blonde.
Descriptive:
* Her hair is a beautiful shade of blonde.
* Her hair is golden blonde.
* She has long, flowing blonde hair.
Figurative:
* Her hair is like spun sunshine.
* She has a mane of blonde hair.
The best choice depends on the situation. Consider your audience and the tone you want to convey.