This Marty has brown eyes. The other actress had blue eyes. And the other one comes back later and has a psychopath meltdown. She also becomes obsessed with John Mcvein. If she can’t have him, no one can.
I hate when they change actors just like this. Better to kill character, sent him to travel or business trip around the world or make little story about an accident with plastic surgery without showing this character for several episodes.