think Barbara appreciated Johnna's help, even though she was so self-absorbed with family issues that she didn't express it very well. But Johnna probably understood.

Barbara definitely showed her kindness.

One thing you'll note is that
Violet never refers to her by name until the very last scene. Once she's alone, she calls up "Johnna! Johnna!" but up til then, she'd only referred to her as "The Indian woman who lives in my attic."
In the stage version you don't get to see Barbara driving away, you just see Violet left alone with Johnna in the house. The last moment of the play is
Johnna cradling Vi in her arms singing "This is the way the world ends" as the lights fade
. You see that Johnna is ultimately above the bad behavior of the family she's been working for and, being the outsider, she's able to be understanding and forgiving of Vi when she turns out to be the only on Vi has left.

It might be that she has become an adopted member of the familly, might it not ?
So, she gets unfair treatment, like anyone else in the group.
That remark about her beauty sounds like the remark about the niece womanhood. A challenge as well as a welcome.
Manelle
"to tax and to please, no more to love and to be wise, is not given to men"