Unless you are engaged to an EU Citizen (not British citizen in this situation!) with a five year residence permit you must apply for entry from outside the UK. If you wish to apply from within the UK in other circumstances your application is likely to be refused unless you can show exceptional reasons why the application should be granted.


So according to this you could save yourself lots of hassle .If you have 5 years residence card you could apply within the UK(she doesnt need visa to come to UK).I dont know if this works in practice.To be on safe side you could aske here @
http://www.ind.homeoffice.gov.uk/6353/1 ... eapr07.pdf

 

The Registration certificate is not a condition for any residence status,it is only confirmation of your status.Provided you are exercising your treaty rights-Worker,self employed e.t.c.Your payslips and P60 are enough proof of your residency rights an EU citizen.

 

As I pointed out if you had a residence card she maybe able to apply for COA within the country.I really dont know if this would work.You could ask,numbers are in the link I posted.
Otherwise as BB said you would not need much to provide,p60`s, payslips and accommodation details would be suficient.