I don't think someone can be "tricked" into falling to the dark side. Manipulated into a certain state of mind sure, but not bent against their will.
Mind you, the nature of the dark side and what it means to fall has never been fully explained (neither has the light side come to that.) I think even Lucas has changed his mind over the years since I'm pretty sure years back he described the relationship between the two sides as being like a parasite vs. a symbiont. That the dark side acts like a cancer on the light and must be destroyed to restore balance. But then there's the mortis story arc which presented the relationship much more like a Zen Buddhist yin/yang, life/death arrangement where too much "light" was just as dangerous as too much "dark".
I think some EU authors have also interpreted it as being as simple as a reflection of the emotions with which a person draws in the force. But I think even that's been contradicted.
As for Barris, if she was still in prison when order 66 came down then it's even money as to whether or not she survived. Most likely she was killed in her cell by clones, but it's possible she was able to escape. That's assuming Palpatine didn't try recruiting her in some capacity.