LaGuardia to NYC traffic is always tied up, trust me, so taking a helo into NYC is a good idea. Her passing in a motorcade on Manhattan would really only screw up a few miles.
White House to Andrews AFB is barely 15 miles by CAR.
FIRST job is SECURE transport. SECOND job is SAFETY. THIRD job is comfort.
Traffic from DC to Andrews is often bad, especially on Friday afternoons! Fifteen miles coming out of DC is a long way. I do think this will mess up traffic there.