
Unfortunately your phrasing is ambiguous.  Re-writing more carefully, we have
(at least) two possibilities.  The first:

Things called "Mercedes" are cars
That girl is called "Mercedes"
Therefore that girl is a car

That is entirely valid as a piece of logical deduction.  It is not sound,
because the first statement is false.  Similarly, I would hold that Jim's
example is valid but not sound.

Another possible interpretation of what you wrote is:

There exists at least one car called "Mercedes"
That girl is called "Mercedes"
Therefore that girl is a car

-- which isn't valid.
