We're led to believe the strangulation occurred outside the wine cellar I believe. That is where the paint supplies tray was situated, taken there before Christmas by the house help, containing the broken brush tip, and a urine stain was found on the carpet. JonBenet also had urine stains on the fronts of her knickers and her longjohns, suggesting she was laying face down at that point.
What puzzles me, is why JonBenet didn't let go of her bladder when/if she was first struck on the head and fell unconscious so that she appeared to be dead.