More about Sophia here: http://en.wikipedia.org/wiki/Sophia_Dorothea_of_Celle
Currently all her WikiTree IDs use Celle or of Celle, but that's just a place, not a house or anything as clearly surname-like as that. Wikipedia only lists Hanover for her house, which I think she just married into (but maybe she was born into it too? I'm not sure, but her husband was a Hanover and they were first cousins.) Her father was in the House of Welf.
I would say Welf.... or Guelf or Guelph... "The House of Welf (historically rendered in English as Guelf or Guelph" according to WikiPedia... so I would definitely give her a house LNAB of her fathers but... not sure which of those would be proper.