As Rayna said:-
- she is the holder of a UK visit visa which means she not allowed to marry as per the declaration made and signed when making the visa application.
- She does not hold the correct documentation for the authorities in UK to legally perform a marriage
- She would need a Schengen visa to enter an EU country which she would be unable to secure here in UK as she does not have leave to remain for 6 months or more. She would need to apply and be granted a Schengen visa from Philippines to be able to enter an EU Schengen country.
I don't know the full requirements for getting married in the EU but unlikely that a temporary visit/tourist visa would be accepted.
There's no problem to get married in any country provided she has the correct visa.
For UK that would be Marriage Visa. Not Visit Visa.
Of course it IS possible to get married illegally, but then living a completely illegal existance as an undocumented immigrant isn't a good start to married life.