our foster girl did it at 16 or 17 years old ... she just did it through via a deedpoll change of name. I signed a stat dec in support of it, and they called me to speak to me personally ... but I'm not sure whether they wanted to speak to me as hher carer, or as her lawyer.

(she wasn't changing her name to my surname - long complicated and painful story as to why she was changing her name, but she was completely doing the right thing to take care of herself emotionally)

but I second persephone's comments regarding doing an affidavit setting out your efforts to contact her biological father to notify him, and your reasons for thinking that's his last known address.

you just need to satisfy the court that it would have come to his attention, or that you've done everything reasonable to bring it to his attention.

these days, contact can involve email, sms, facebook even, so be creative

and the affidavit can just be in your own words - you don't need to use lawyer-y words for it. just say what you tried and why, what times you phoned, when you posted the letter, etc, and staple a copy of the letter to it.

the registry at the court or your local police station should be able to help you out putting it together, and they also should be can witness the affidavit for you, if you don't want to incur legal fees for doing it.

HTH