Does this bonus only apply if you book the flight yourself i.e. through your own BAEC account?

e.g. my BAEC account is (currently) domiciled in the UK. Mrs Shorthauldad's account isn't... it's in one of the qualifying countries.

If we travel together e.g. FRA-LON-FRA in CE then does it make any difference if I book a trip w/ her as an additional passenger or vice versa?

All other things being equal, I'd book it through her account to be on the safe side ... but then we don't benefit from my status on the booking, do we? ...or do we?