Hi Mick,
Once you've reported the situation to them I'm pretty sure her visa will be cancelled, but apart from that fact being recorded on a database somewhere, I'm not sure what else would happen. They might write to her at the address the visa was despatched to informing her that it has been cancelled but who knows.
If she decided to come here, with a valid visa in her passport, she probably would be allowed to board a plane in Manila and would probably be able pass through immigration in the UK without a problem. Even if immigration in the UK stopped and questioned her, she could say she was still living at your address and that the reason she had gone home so soon after arriving was to attend a funeral or something.
From what I've gleaned from watching UK Border Force on the telly, they don't tend to look things up on the computer unless things don't look quite normal at first glance.
It might be a good idea when you do contact UKBA to ask them what steps they are likely to take to stop her re-entering the country.
Iain.
I presumed that when a UK issued machine readable passport/visas get scanned that your status is checked. Or does it just record the fact that you entered?