Everything is possible, but here's what I am thinking. If it was intended to be a robbery, why was nothing taken? Your average burglar would have grabbed her purse and some jewelry at the very least, and maybe some larger items like a flat screen TV if he had a large vehicle and some time to work. He would have subdued the victim with ropes/tape/zip ties and something over her mouth to keep her quiet, and left her at the scene. But... did she know the masked intruder? That would be the only reason to remove her from her home if robbery was his motive. Robbers rob. They don't want to kidnap or murder, IMHO.
This feels more personal. Is someone holding a grudge against NG or one of her family members? Does the kidnapper have some twisted agenda?
Someone upthread mentioned the potential of a crazed stalker. I mention it because it's in the realm of possibility, but it's not my favorite theory at this point. Note that I have been wrong many times.
Stating the obvious here, but kidnappings are rare in the 21st century in the US. Why NG? I hope we will have answers soon. And my prayers are with her family.
All MOO