Are you suggesting she just overstays here on a visit visa?
Or am I wrong again?
It's really not rocket science, it's very simple.
As I said, they can get married in any country provided she has the correct visa.
If she had a UK marriage visa she could get married here in UK.
If she was the respondent in the UK divorce it's quite easy to have that legally recognised in the Philippines then she'd even be free to marry in the Philippines. Period.