The easiest way to obtain the CENOMAR as lastlid says is online at the ecensus website but allowing it to be delivered to the Philippines, you then get a reference where you fiance will goto the local bank and pay in the money. About 2 or 3 days later she'll receive the CENOMAR.
There is the option to pay by credit card, and have it sent overseas, I haven't tried this but can foresee complications.
As has been mentioned regarding the CNI, you first goto the registry office, submit your application and wait 21 days and voila you can collect the CNI.
The CNI when used in the Philippines is valid for 3 months, so you must take it to either the British Embassy in Manila or Honourary Consul in Cebu to have it converted into a local document before that 3 months is up. You need to make an appointment to complete this part, and sometimes its done the same day or sometimes the following day.
You then need to submit this with the other documents to city hall and wait another 10 days for your license to marry.
Essentially it takes some careful planning to get the timing right.
