for me, most of the time, making eye contact just feels too "personal" like the other person can see exactly what I am thinking or read my mind. It is uncomfortable in most situations, and I have to think about it to do it "correctly" like at work (retail):
Look person in eye, say "hello, are you looking for anything in particular today?", smile and nod, lead to item or let them know that if they need anything I will be right around the corner.
I have recently found out that not everyone has to remember the steps each time and THINK about making eye contact when saying hello to someone. I have also recently found that I stare at a speakers tie, or shoulders, or earrings when they are speaking. (mostly at least.) Instead of forcing her to look people in the eyes, I would just let her know that some places are not polite to stare at if she gets in that habit. Possibly make her FACE you, it's hard to hear someone when they are turned away from you. My kid is a spinner, I have to make him face me when he talks "honey, I seriously can't understand you when you are not facing me, stand still a sec, and tell me again."