Letting Sally make the decision is a great suggestion (she’ll choose to stay though, since she considers herself to be more Button’s family than John is tbh). The friendship between Sally and Button is very much meant to be family-esque from Sally’s side. From my personal experience with long-term friendships, the relationship becomes one where there’s a sort of . . . presumptive behavior from both sides? The dynamic is very “Shut up, I love you, let me grab my bag and I’ll be over asap. No, stop talking, I didn’t ask for you’re permission, I’m coming over because I know you and you need me.” (I’ve had the same best friend for two decades, and although obviously all relationships are different, Sally is very much the kind of person who falls into that dynamic.) She’s also not going to hang around someone who’s still neutral about her after over a decade of friendship.
Of course, that presumption on Sally’s part doesn’t seem to quite work in-game right now since, unlike Button, players have only known Sally for a few scenes as opposed to years. Which means I need to better refine and convey their dynamic, since right now it appears that a lot of people read her as aggressive and uncaring rather than as a long-term friend who honestly kind of just has a forceful personality
Letting people chose whether they’re comfortable with this type of relationship is the best I can do and still be true to the characters, since unlike K/Glitch/Rosy, Sally’s known the main character for over half their lives.
Sally is pushy and decisive but it has more to do with her personality and the fact she basically considers Button to be her platonic other half, rather than because of Button’s limitations (Button may not read it this way, obviously!).
That effects it somewhat, although Button is a preset enough character that Sally will always genuinely like them in the beginning. Pushing her away when she’s no longer useful, however, informs for Sally that, despite her best wishes, Button doesn’t really consider the dynamic between them to be the same kind of friendship that she does.
Definitely later, but right now Grayson is kind of busy handling the fallout from well

EDIT:
Also, I don’t take personal offense to people who dislike Sally. She, like all the other characters, has a strong personality, which means she won’t be everyone’s cup of tea. She’ll sometimes rub the wrong way, and that’s perfectly fine! My goal is to make certain that character intentions, at least, are always clearly conveyed. Which Chapter 4 failed to do and thus is being reworked 
People who dislike Nick, I have more complicated feelings towards
