Observer A might be behind the ship.
In which case she would never see the ship, or even know it was there. Here I use “see” with due deference to Paul’s comments.
It must exist, since it has infinite relativistic mass. But just how it would exist is a problem. That's what happens when you try to think about things that can't really happen.
True, but I’m quite happy with that, as I was looking for/at reasons why massive objects might not be able to accelerate to c.
As you might suspect; the concept of infinite relative mass interests me. I’m trying to get my head round all that it implies.
In the RF of the ship Observer A would be traveling at the speed of light. So the problems would be reversed.
So neither would see the other, and both would measure the speed of the headlight as c; except that they would not “see” it, so could not measure it.
As you say: that's the problem with impossible scenarios.