As others have said, a visit visa is almost impossible for a filipina. She would have to convince the authorities that she would not overstay in UK and that she would not need to be in receipt of any state funding during her stay.
Much better to come here and visit - you will almost certainly enjoy your stay here. Yes, you can stay for up to 21 days without a visa but, even if you don't obtain a visa before you leave UK, it is very easy to extend your permitted stay once you are here. Whereabouts does your lady friend live?
Read through past postings in the forum to find a lot more advice - such as: Don't consider bringing Traveller's Cheques. Don't even buy pesos in the UK - the exchange rate will be very poor. Bring sterling cash - there are money changers everywhere, giving better rate of exchange, and bring your debit card (preferably a Nationwide card) - you can draw from most ATMs.
