Hi Where are you bringing her from? We brought ours back from HK to the UK, she stayed for about 1.5 years. In terms of visas and legalities it was not a big problem - we had to write a letter stating what we paid her and that she would have a bedroom and bathroom for her own use in our UK home. She was issued a visa quite quickly and apart from a long time to get through immigration - she had to be interviewed - it was really simple. This was in January 2006 though so the rules may have changed.
The problem we found, however was with settling in to the UK. She had been back with us before, the previous summer for a couple of weeks so it wasn't completely new to her. We lived in Sussex, about 45 min from London by train. Nearby there were only nurses of her nationality who were not very friendly towards her so she was not able to make friends locally. She did not drive which was tough in the area we lived in, she found the weather difficult. Our relationship with her changed quite a lot after we moved as she wasn't happy.
After 2 years she could have extended/changed her visa to be able to take any job which we were happy for her to do as by then both our daughters would be in school and she seemed to be happy for that opportunity. Then, out of the blue after 18 months in the UK, she said she was returning to the Philippines to get married (we had no idea she even had a fiance as she had never once mentioned it!) and asked to bring her husband over to live with us after the wedding. At this point we had to say no and end the arrangement when she left the UK to get married. We had known her for 7 years by this point but we could not have a complete stranger living with us and being sponsored by us too. She left on a good note and we are in touch still but the last 18 months just wasn't the same as when we were in HK.
I hope this helps, I guess it might not if the immigration rules have changed by now.