The level of support that this game enjoys makes it pretty clear that the Sandra, Haley, MC path is quite popular. As Walter points out that path is pretty much canon. So despite the vocal part of the fan base that disparages Sandra, they are almost certainly in the minority.
My goal, as is Haley's goal, is to end up in a long term sexually and emotionally intimate relationship with my fraternal twin. By far the simplest path to that end is to find a compatible soul who we, my twin and I, can seduce into a menage a trois, a "household of three". Now as it happens, I find Sandra, for all her obsessions, quite attractive. While we've yet to see the epilogs, it appears that Haley and I have succeeded, and Sandra will only ever know love, support, and every good thing I and my sister can give her. You see I do love her, I just love Haley a good deal more, and Haley and I will ensure that none of us ever have to choose between us.