I know what you mean lordna, but just allow me some brainstorming and see what you think.
You are all living here in UK.
As a British Citizen, Deed poll is allowed and recognised (even by the passport office too).
As a registered British Citizen your step daughter would have sufficient documentation to be known by whatever name she (you) chooses.
There would be no real need for her to have a Philippine Passport at all at this time.
(My wife still did not yet renew her Philippine passport.)
So, I'm just wondering what it is that the Philippines/Philippines Embassy will not recognise?
Her British Passport? Her Naturalisation Certificate?
They don't do that anyway unless a new Oath Taking has taken place at the Embassy.
At some time she may well wish to make an oath taking to re-acquire Philippine Citizenship.
But that all in the future, and besides her Philippine Naturalisation Certificate will be sufficient for her to enter Philippines as a Philippine citizen even with a British Passport.
Sorry just thinking out loud.
I don't know how many twists and turns are involved with adoption, but it sounds like it might be a very challenging process.
Just trying help.