Oh she changed. It was a complete 180 from what she was before though, going from a relatively nuanced character to "MWAHAHAHAHAHAHAHAHA I'M EVUL HOR HOR HOR!!" It's not that she didn't change, it's just that her change was fucking stupid.
She had no reason to do what she did to the protoss in brood war at all. Yet she twisted the knife in for sadistic amusement. That doesn't scream "I'm never going to let myself be abused again." That just screams HOR HOR HOR I EVOUL.
She DOES change in Heart of the Swarm overall
In the intro missions she's conflicted; she wants to make Mengsk suffer for his crimes but at the same time she's scared of the darkness within and open to the idea of leaving it behind and having a normal life, as demonstrated by these pieces of dialogue
1.) Cinematic - TransmissionEdit
Transmission SC2-HotS VCine102:59
Transmission SC2-HotS VCine1
Kerrigan: Jim? Are you on this frequency?
Kerrigan: Jim, are you out there?
Kerrigan: I´m at the rendezvous, it´s all clear here.
Kerrigan: I´ve been thinking about what you said.
Kerrigan: there´s something dark in me, Jim…
Kerrigan: I need you. I need you to hear me right now.
She aims her gun at the zergling and after hearing Mengsk's gloating, she has an emotional outburst and then seems angry and determined when saying "confirmed".
2.) Kerrigan: "Kill them all. No one gets out alive."
Naktul: "Yes! The Queen has returned. Kill the Terrans."
Kerrigan: "The Queen? You're right. I was slipping back into something that-I have to get out of here."
After Mensk's evil gloating about Raynor's death, she's in an "ends justify the means" mode. She feels guilty about what she did to Lassara and doesn't take pleasure in it (and angrily tells Izsha to shut up when Izsha asks if killing Mengsk will bring her joy.) However, she's willing to do WHATEVER it takes to get revenge.
After Zerus and Char, though, things begin to change. She shows mercy to Warfield's men rather than simply slaughtering them, and if you look at her facial features from 1:50-1:57 in the following link https://www.youtube.com/watch?v=pzT2mUTFwH0 you see them softening as she carries out the command. She's no longer cold like she was in the 1st part.
When Mengsk tells her "That man sacrificed everything to give you back your humanity. And you threw it away. How he must be disgusted by you. Why he'd be the first in line to kill you." Kerrigan looks.....upset. It's pretty clear what mengsk said rings true, and she's starting to realize how selfish she's being. She also spares Stukov in spite of their past history.
When she and Raynor meet on the Moros and Raynor asks "What have you done?" The way she says "What I....had too." makes it pretty clear that at this point she's trying to convince herself. She was pretty resolute on Kaldir, but now she's rattled. Her faith in the justness of her actions has been undermined. Finally, on Korhal during her conversation with Valerian she doesn't notice Raynor and was shocked by his arrival in such a way she REALLY didn't expect it. That implies that a.) she didn't agree to spare civilians just to please Raynor and b.) Kerrigan DID ultimately agree to spare civilians because it was the right thing to do.
Kerrigan at the end of Heart is NOT the same as the Kerrigan at the start. She actually evolves and grows over the course of the story, starting as a conflicted individual, than a vengeful warrior hellbent on revenge and fuck the consequences, has a heel realization and finally settles as an anti hero who isn't nice but gives a shit about life.