Hi Tuft,
Your gf doesn't have much chance of getting a tourist visa unless she has a well paid job, money in the bank and property in Phils. Without these things, the UK Border and Immigration Agency will assume that she is unlikely to return to Phils when her visa expires.
So it looks like, if your really serious about the girl, then you'll just have to bite the bullet and start planning to get married in Phils or apply for a fiancee visa to bring her here to get married in this country.
Most of the guys here would probably have liked to bring their gf's or fiancee's over for a visit first before getting engaged or married, but as I said before, very little chance of getting a visa unless they are quite wealthy by Philippines standards.
Cheers,
Louella & Iain