Hmmm, for some reason you cut it off right before the crux of what's being discussed. If it ended where you posted I'd love it, but it didn't end there. It continued which is important.
What happens right after is: (screen darkens_)
"Say....Harry...
Do you think you can forgive a cheater and a murderer...?
...I know I wouldn't"
And last line is italicized showing it's importance. Why include it and why italicize it? Because it's important to who Laura is and how she now sees the world in her deepest throughts.
For the record, I would prefer your interpretation in the scenario, it's nicer but this game isn't nice. There is no happy ending for the two of them though I really wish there was.
First remember that Laura looks at herself as someone dirty compared to Harry, Harry is the ideal she would like to become.
She asks if he would forgive cheater and murderer ... does she consider circumstances in that statement?
Harry ultimately already forgave her for cheating or doesn't even consider her to be cheating to begin with. He chose to believe in her through everything, he chose to believe that there is reason in what she is doing and the she wouldn't hurt him otherwise.
So the question really becomes about the murderer part - but again is that something she needs forgiveness for ? Being the victim there and trying to protect loved one i think for most it classifies as self defense.
I believe Laura already knows that Harry will forgive her but she nonetheless feels disgust with herself that she ended up hurting Harry and killed a man. That is why she puts emphasis on not wanting to forgive such person, she believes she doesn't deserve forgiveness. But at the same time she wants to be like Harry right ? and Harry will forgive, hopefully she will understand that her desire to self punish herself is at odds with Harry happiness.