I got my negative test in the morning, then paid for an additional night. I was free to go out and come back in my room anytime in the quarantined floor.
it's not that they worded it badly, it's just that the developers wrongly made the field mandatory to all applicants when in fact, it's just aimed at foreign residents to upload their resident card.
If Spanish doctors were not allowed to do it, the local embassy would know that all certificates they receive are fakes. I'm sure her doctor is a douche strict on rules that don't exist.
Just for your info, in the USA you don't have transit zones in the airports. Everyone has to pass the custom and enter the US even for just a layover (and hold a visa if their nationality request it).