There are two ways in which your wife can apply for 'Further Leave to Remain'. She can either post her documents to the UK Border Agency in Croydon ... OR ... she can schedule an appointment at one of 7 PEOs dotted throughout the country.
Obviously it will be a little more costly to apply in person ... but worth paying that bit extra for same day service, if another member's recent experience is anything to go by.
The thread I'm referring to here is entitled Public Enquiry Office - Liverpool (FLR) posted by axelandpixel on August 14, 2010.