After her first encounter with the Dalek, one has to assume that the Doctor fills her in on the Time War in more detail, especially detailing the evil of the Daleks. Rose experiences it firsthand when she gets caught by the transmat beam and placed into the game show in Bad Wolf. Thus when she comes face to face with the Daleks she certainly will believe everything the Doctor told her about them and one believes she'll do anything to save humanity from them. Additionally, in the second part of this two part episode, it becomes fully clear that Rose is in love with the Doctor. She's willing to do anything to save him, just as he is for her. There is a sense in which she is to be lauded. She probably did end the situation with the least amount of violence possible and saved humanity. Additionally, she brought Captain Jack back to life. Her ingenuity and dedication to the one she loved were exemplary. It still was a decisive act that changed her forever and made her like the Doctor. Rose became, in some sense, a killer.
As things move along in season two, we start to see Rose becoming more and more like the Doctor in some respects. Tooth & Claw is a particularly fascinating episode. What you can't help but notice is the similarity of attitude between Rose and the Doctor. The Doctor's great weakness is arrogance. With him at her side Rose clearly feels invincible and finds all of the danger quite a bit of fun. This leads to their downfall. Their attitude, particularly Rose's, leads the Queen to open the Torchwood Institute, the organization that would eventually tear them apart.
At the end of season two, the Doctor and Rose are separated for good, so it seems. Rose is trapped in a parallel world. She gets stuck there because of the aforementioned Torchwood. Torchwood was created by the Queen in response to the alien menace, the Doctor included, and was very militaristic. When the Doctor and Rose arrive at the end of season two they're harvesting energy from a hole that had formed in reality. While in the process of closing that hole, and sucking the Cybermen and Daleks into it, Rose and the Doctor get separated for good. Here's where things take a surprising turn. What does Rose do with her life while in the parallel universe? She works for parallel Torchwood, because she knows so much about aliens.
When you put all of the pieces together you can see how Rose becomes a soldier in season 4. While travelling together she has made the Doctor more compassionate, but her experience with him has hardened her. Additionally, perhaps because she is so in love with him, she never questions him. She laughs in the face of the Dalek, displaying the same vitriol as the Doctor towards his arch enemy. In essence, she has become just like the Doctor, and while he never carries a gun, that's about all that separates him during the first two seasons from being a soldier. Working for Torchwood simply finishes off her transformation into becoming a soldier. It's not that big of a surprise when you stop and think about it.
So is the Doctor responsible for Rose's transformation? Again, I would say yes and no. He's the more violent one at the beginning of their travels. He's rather merciless. That clearly impacted Rose. His arrogance also rubbed off on her and they both were culpable for the creation of Torchwood, though Rose more-so than the Doctor.
It's their separation, that I believe ultimately pushes her over the edge. She has a frantic desire to reunite with the Doctor at any cost. Additionally, she's away from his influence. Even though the Doctor is violent, he is far more judicious and more merciful than UNIT or Torchwood. He's not there to provide moral compass and Rose is simply in over her head, as is the rest of humanity.
 I must say, though, that I did enjoy her exchange with the Dalek in this scene. :)
 If you haven't seen the episode, the Daleks control humanity through a series of game shows like Big Brother and Weakest Link with a twist. The twist being death if you lose.
 The Doctor's interest in her was first made explicit, surprisingly, by the Dalek in the episode Dalek. That the Dalek's claim was correct is made crystal clear in Father's Day.
 In the final three part episode of season three there is a lengthy discussion between Captain Jack and the Doctor of this incident. The Doctor still remembers it with admiration, calling it 'so human' and meaning that it exemplified what makes humans great and why he loves them. His solution would have been catastrophic. Rose saved his life and the lives of many. I think this episode may be a good test case for just war theory. If ever violence was permissible, it was here. Additionally, that statement makes me wonder if we are supposed to understand Rose as the paradigmatic human in some sense, and her relationship with the Doctor as paradigmatic of the Doctor's relationship with humanity. Perhaps I will explore that some other time.
 His arrogance bites him again in a big way in the post season four special, The Water of Mars. In the future I may explore this group of specials. They explore the Doctor in a more probing manner than anywhere else under the writing of Russell T Davies.
 In that episode I alternate between finding her impertinence hilarious and irritating, and I'm a fan.
 This isn't blame on the Doctor, it's noting the causality of her experiences with evil and danger. As we see with humanity as a whole on several occasions, threat of death often brings out bad things.