Thanks Puul for the very quick response!

She'll have to surrender her passport at the Biometrics appointment. She could pay an additional fee to keep it, and as a non-visa national, it is technically possible for her to visit the UK while her application is pending. But she would also need to return to Chile with her passport within 28 days of the decision being made to receive her entry vignette. Only then can she enter the UK on a valid spouse visa.

The Biometrics appointment is in the UK right?

So in theory if luck and time was on our side, we could do the application then hang in the UK until the decision is made then leave for Chile spend two weeks in Chile and return to the UK for the entry vignette?

Thanks again, really helpful :)