Hi Ivor,
welcome to the forum, it is understandable that you have some concerns about the interview and everything that is involved.
There is a lot of info on this forum if you get the chance have a good look through it, also pete here has a link to his website that has generally what you need to know about how to prepare your wife "to be" for the interview.
Actually ivor here is the link below for pete's website so just click on it and have a look...
http://www.british-filipino.com/
John