Sponsor letter?

if your applying for settlement you will need to meet section 281 of the immigration rules, you need to prove your able to support her without any government funds, prove you can house her and yourself and any dependants, ( they will only except a proper doent saying the size of property you live in, don't bother sending a letter from yourself saying the size of your house) prove you've been in contact, look on ukvisas, they tell you all you need to know, good luck