Okay so if I'm reading Terezi's intent right, I think she's trying to nudge the timeline so that her abusive relationship with Gamzee (and/or her relationship problems in general) doesn't happen and the associated depression that led to her getting her eyesight back, and the WORSE funk she got into after that.
Of course I realize that "him" is referring to Karkat, but I'm thinking on the long term here. Not having that same relationship as in the original timeline is probably going to change Karkat in some way too, but I haven't quite figured how yet.