Stepsister Masturbates in Front of Stepbrother

Your stepsister wants to spend the night in your room since the neighbor's party is so loud. She insists on staying in same bed too. Soon you realize she's masturbating under the covers. That is so weird! What should you do? She suggests you both could masturbate so it would be less weird. Can you handle that? As she gets naked right in front of you, the only question is where are you going to shoot your load. She has a good idea for that too...