For me unless there is telltale sign its hard to tell if something was shot separately as a different element, unless it draws attention to itself.
I have no way to know if Amy was shot separately from Ewan, but sure looks like it.
A little like this from The Phantom Menace (though could also just be an oversight)…
Note the orange glow of the CGI molten metal reflecting off the blast-door and onto the floor - and yet Obi Wan Kenobi is standing in the way of that actual reflection:-
^ 1999 theatrical release
^ 2019 UHD release (droid parts were added on the floor to ‘lessen’ the effect of the molten metal reflecting onto the floor?)
All credit to Phase 3 for that one. 👍