There was a lot of ways that Margaret could have responded to this. Fear. Anger. Rejection. Denial. Outburst. She could have been angry at Kaguya for having placed her in this situation; she could have expressed her fear of being trapped inside of another being or any other myriad of pathetic, weak willed reactions. She would not do any of those. Instead, she closed her eyes. 

"...inside of you?" she repeated to make sense of the situation. Arrancar and Hollow abilities were diverse and varied. Who knew? "...is there any way to get me out?" she asked, beginning with the logical and reasonable questions.