It's all right if your style is more introspective. So, for example I think it was in Chapter 3 that:
- Ally is reminiscing, or brooding; kneeling and crying.
- Samantha puts her hand on Ally's shoulder
- "Samantha had removed her hand from Ally’s shoulder as if it had caught fire." That's a good line, very descriptive and concise, especially contrasted with Samantha's expressionlessness
- Ally stands up to interrupt Samantha with something she knew from having special abilities
- Ally doesn't like that she just did that, and Samantha knows that Ally just did that special abilities thing
- Samantha tries to be casually dismissive
- Ally is not consoled
So, there's a lot being communicated that is not a part of the dialogue tags because of the way that they are interacting, and that makes it a good scene.
The scene that you're asking about:
-
Samantha smiled half-heartedly, “So, that school was bad to you too.” That's Samantha approaching a painful memory with levity, but in a subdued way that's true to Samantha's sort of frigid personality.
-
Ally shook her head in disbelief, “Mr. Garcia assumed that powers equal bad.” Paraphrasing what you actually wrote only because I think I'm writing a very long comment…but, same, this shows that Ally is only beginning to make sense of her life, because she's shaking her head in confusion rather than disapproval of what happened to her. That also keeps with her character.
So the next two lines don't have to continue the pattern of body language, dialogue, action, dialogue. I know some readers who don't like that because it makes the characters seem fidgety, or they notice the literary technique as glaring, so to them reading that pattern starts to feel fake. Sort of like how my 10th grade English literature teacher…didn't tell us that exclamation points or interrobangs were not allowed, but she did warn us that they were cheesy. A dialogue tag other than 'said' can also be glaring. Similarly, some readers think that body language is cheesy, but I think they're a good way to add subtext to what the characters are speaking out loud. There's a place for dialogue tags other than 'said', and there's a place for interrobangs and exclamation points. So to continue the scene:
-
Samantha: I knew that you were angry with me after finding out, but I didn’t realize you took it out on them. They didn’t deserve that. They were only looking out for you.”
-
Ally: If they really were trying to protect me, then I wouldn’t have been stuck living here in this god awful place for twelve years with you,”
There are many ways that Samantha can say that same line, and many ways for Ally to respond with that same line, and many ways that they can influence each other.
Samantha's Set-Up
Samantha could sort of walk around mumbling vaguely, "I knew that you were angry with me after finding out, but I didn't realize you took it out on them. They didn't deserve that, they were only looking out for you…" like it was a long time ago and it can't be fixed anymore, and she's tired of hearing about things she can't fix but she's moved to say something, but she doesn't want to be responsible for what she says, so she moves around skittishly sort of putting things in order that weren't out of order and doing small chores that don't even really need doing.
Or Samantha could be more gentle and emotive. Still with the wry gallows-humor smile, "I knew you were angry with me after finding out, but I didn't realize…" and have her shake her head and look Ally in the eye, "You took it out on them? They didn't deserve that."
Or Samantha could be self-righteous, as though she wants to grab Ally by the shoulders and shake her, so the subtext of that same line is 'What's wrong with you?!??'
So with that lattermost interpretation, Samantha could be standing up and slamming her hand on the table. "I knew you were angry with me after finding out, but I didn't realize you took it out on them." Samantha's voice shook with rage. "They didn't deserve that. Look at me, Ally. They didn't deserve that. Do you understand? They were only looking out for y—I told you to look at me when I am talking to you!"
Ally's Payoff
Depending on how Samantha is acting, Ally can react or respond differently. With a tired Samantha who wants to check out of life, Ally might want to wake Samantha up, hold her accountable, and not let her escape or deflect the impact on Ally's life by mumbling or skittishly doing random chores. Ally can be the one taking the dustcloth away from Samantha's hand, looking her in the eye, and then saying, "If they really were trying to protect me, then I wouldn’t have been stuck living with you."
To the gentle, emotive Samantha, Ally might deliver the same line but more deadpan, sort of like a way to say, 'Don't you dare get even a little bit self-righteous or fake-concerned, because I am dead inside and it's because of you and them.'
For the latter, it might be appropriate for Ally to escalate the violence, like screaming her line in response while pushing nearby furniture upside-down or something.
Or mix-and-match.
The line that you're asking about, I read as deadpan.