My friend says she wants me to describe her in one word and I think she does not care about anything most of the time. So I'm looking for a word that describes that.
I can't find a noun for that. But I can think of some adjectives:
Apathetic derived from ODO
Which not interested or concerned. Having or showing little or no emotion.
The synonym may be:
Which means lacking physical sensation or sensitivity.
Which means having no particular interest or sympathy; unconcerned.
Carefree — M-W
adjective having no worries or problems : free from care
"She has a carefree attitude toward life."
"They spent a carefree day at the lake."
Free spirit — M-W
noun a person who thinks and acts in a free way without worrying about normal social rules
"Their daughter is a real free spirit."