And Kaidan looks back, reflects on everything, and takes a much more thoughtful and taciturn approach to the events and morality of the series.
Ashley doesn't. Once her mind's made up, it sticks. And she's not the kind of person who thinks she's wrong. She's right, you're not, end of story.
From ME2:
Subject: Hey there.
Shepard,
I'm sorry for what I said back on Horizon. When I lost you two years ago, it tore me up. I prayed for you every day. I read a lot of Tennyson, thinking about you, just like I did when my dad passed. And then you came back, and it was like my prayers were answered. But I'm not who I was then, and neither are you.
I don't know what's true anymore. Part of me can't believe it's really you. I keep going back to that night before Ilos, our night.... I haven't let myself think about those memories for more than a year now.
I wouldn't have expected you to work for Cerberus, but I know why they sent you to Horizon. I saw how many people were lost there, and if anyone can stop the Collectors, you can. I can't go where you're going, but I can wish you luck.
Just stay alive out there... Skipper. I don't know what the future holds, but I can't lose you a second time.
--Ash
Death closes all: but something ere the end,
Some work of noble note, may yet be done,
Not unbecoming men that strove with Gods.
Worth noting those first two words: "I'm sorry".
Also, during the hospital conversation she is willing to accept that Shepard 'cut all ties' with Cerberus (and having that conversation makes it considerably less likely that she'll refuse to back down later). So... yeah, she can change her mind. I'm pretty sure there was a charm opportunity back in ME1 that would shift her perspective enough to make her one of the characters most likely to support saving the Council (moreso than Liara).
I'd also say that her concerns regarding Shepard are pretty justified. I'm genuinely surprised that TIM didn't have a control-chip installed on the Commander - even if it had been a dormant one as a fail-safe. TIM's probably regretting that choice by the time that Priority: Kronos rolls around.