Bess has a passport?

It's a fair while since I've had a passport, but don't you need a birth certificate to get one? I know her mother took her to Fiji as a child, and got a passport for her, and I assumed that, unlikely though it was, she hadn't needed one since.

However, when Bess queries why she's staying at the hospital, her husband says that it's because she likes holidays in Europe. That being the case, how could she have not seen her birth certificate and thus, know she was adopted?

I suppose the phrase suspension of belief must come into play: if she knew she was adopted, the series would be a non-starter.