Looking on the internet deeply has found these results:

she is sleeping on the bed is the most popular phrase on the web.

she is sleeping in the bed 15,560,000 results on the web	she is sleeping on the bed 16,240,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
I met my wife six months rest of my life is sleeping in that bed. You're sleeping in the bed with me tonight. Sleeping in the bed of the man I killed. They were sleeping in bed when they heard the shots fired. My wife is sleeping in your bed. My morn thinks you're sleeping in the bed there. Until the boy is sleeping in his bed again everyone in this room works for me. Until the boy is sleeping in his bed again, everyone in this room works for me.	Sleeping in the bed of the man I killed. She approached to the Prince, sleeping on the bed... and raised her knife. Could you imagine sleeping on a bed of flowers. I met my wife six months rest of my life is sleeping in that bed. You're sleeping in the bed with me tonight. My morn thinks you're sleeping in the bed there. Martin's sleeping on the guest bed. My wife is sleeping in your bed.

she is sleeping in the bed

15,560,000 results on the web

she is sleeping on the bed

16,240,000 results on the web

More popular!

I met my wife six months rest of my life is sleeping in that bed.
You're sleeping in the bed with me tonight.
Sleeping in the bed of the man I killed.
They were sleeping in bed when they heard the shots fired.
My wife is sleeping in your bed.
My morn thinks you're sleeping in the bed there.
Until the boy is sleeping in his bed again everyone in this room works for me.
Until the boy is sleeping in his bed again, everyone in this room works for me.