M.R.
Awe, poor baby!
I think you already know, the kid is just 18 months and still learning.
If it were my kid, I would be right there with her and when I see her going to be forceful, I would grab her and show her how to touch gentle. I have had to do this with my baby LOTS! It will take tons of redirection and work.
Mom needs to stay on top of it and eventually she/he will learn how to be gentle.
It just takes time.
At this point when the baby comes in contact with people and I see that little "I want to slap you" look on her face, I say "Kay, be gentle" and I can see her face getting calmer and nicer. lol She nuts!