I have been writing.
She has been writing.
They/you/we have been writing.
I have not been writing.
She has not been writing.
They/you/we have not been writing.
Have I been writing?
Has she been writing?
Have they/you/we been writing?
The present perfect continuous tense is used to talk about an action which began sometime in the past, has gone on till the present and is still continuing.
She has been sleeping for four hours.
I have been working in the garden since morning.
It has been raining since yesterday.
In the sentence She has been sleeping for four hours, she started sleeping four hours ago, slept without stopping for four hours and is still sleeping.
Note that we use the present perfect continuous tense to emphasize the duration and continuity of the action.