Done this one a few times.

This is the letter that I wrote for Marvie's first ever visitors visa, I just omitted personal details, so hopefully still makes some kind of sense.
If she has finances to support her trip, then she'll need to provide proof of those. If you're supporting the trip, anything that proves you can afford it would be fine (I provided a few months salary statements)
Marvie also wrote a letter explaining her situation to be included with the application. You will also need a copy of all stamped pages of your passport, and the photopage.

We've done several applications since and obviously built up more evidence and a record of history, but the first is the one you're on edge about.


Dear Sir/Madam

I am writing to support the application of visitors visa for aa. I met aa onboard the cruise ship bb whilst working for cc in dd. We have had a very close friendship, which we hope to develop after she has completed her annulment. In the meantime, earlier in December I came to the Philippines to spend a vacation with Marvinia, and we also travelled together to Hong Kong for a few days.
Although aa has her own finances, I am going to completely support her whilst she is in the United Kingdom. We plan to both stay at my home, and to travel to various tourist sites within the UK whilst staying in local hotels at that time.

I have provided an official statement of my salary from my employer and a printout from my online banking to provide evidence that I can support Marvinia. I am now working as xx on a zz for cc where my yearly salary is ss, and I will be on vacation for the entire period that aa is in the United Kingdom.

If you require further information about our itinerary, or information from me or my employer feel free to contact me on the below contact details: