They basically wanted Theon to find his humanity again by seeing Sansa continually abused.
You saw a character that has her own story line become foil for a minor character to change.
Of course they didn't care about her, she's not the center of the point of the sexual assault, which is the problem in a nutshell really. They put this shit in and then don't really think hard about how it's affecting their own narrative. We'll just make her sullen now since that's all rape does to a person and affect their future decisions right?
It's lazy fucking writing, tropish shit. People don't just harp on tropes for shits and giggles. Well you see when writers/producers consistently rely on them and don't actually write out the motivation for a thing to actually happen or a character to act for a reason other than lulz, you get the schlock you're seeing in parts of GoT. You're also seeing the story go nowhere because it doesn't further the narrative in any way. We already know who's a shit, all they tend to do is reinforce that someone is even shittier this season. Oh okay, congrats, yawn.
With characters like Ramsay and Joffrey you might as well have some cartoonish voice say "WAIT TILL YOU SEE WHAT HE DOES NEXT", I mean come on.