よけいなことなのかな。 I wonder if this is unnecessary.
もう朝なのかな。I wonder if it is already morning.
彼女は何も食べたくないということなのかな。I wonder if she does not want to eat anything.
I feel that these sentences are mostly used when you are talking to yourself.
They can be spoken by both men and women.
よけいなこと in this case is more likely "something inappropriate because it is too much or overdone"