I think that good vs. evil is very developmentally appropriate, especially in pretend play. It's great to mention it to her. The comments you're making might now immediately translate to the way she plays or the responses you get from her, but you are planting the seeds. I would be aware of whether or not she things of her classmates or friends in terms of good guys and bad guys. My son doesn't seem to say those things about his classmates, unless he's talking about playing Spiderman at recess.
At 4 years old the rules of life are very cut and dry, very simplistic. We can talk to them about why things are wrong, but by and large they respond to "because that's the rule." We need to keep in mind that as children grow they need to begin asking why and understanding why.
I went to a Catholic high school and took religion classes (and morality). Those classes are huge! High school students need to begin to challenge what they have learned. They need a safe environment to ask the difficult and challenging questions. They need to be able to question what they have been taught so that they can choose it for themselves. I felt so fortunate to have parents and teachers that recognized that and gave us the freedom to challenge and to disagree.
I hope that that didn't seem like too much of a tangent. I just wanted to say that this is ok at 4 years old. As she learns and grows it will be healthy for her to think about things as less cut and dry and recognize that there is good and bad in all of us. It is our choices that help form us. We can always choose good or choose bad, so there is always hope!