OK lets cut to the chase. So are you saying that she has already submitted her application online then submitted her supporting docs at a VFS application centre and has now been contacted by the Embassy Manila Hub to attend an interview ?
To the best of my knowledge there has not been any interviews at the Embassy for visa (including Spouse or Fiance(e) visa) for many years now.
Occasionally the Embassy will contact the applicant to clarify some issues or missing information by phone, e-mail etc but not usually.
Can you please clarify the reason for your question regarding interview at the British Embassy ?