There is actually another thing that made me consider Sage being in on it in some way as well, and that is the entire party-with-the-preps-thing. Something about that doesn't quite add up for me.
The official reason for that that Quinn (and I think Sage too) gives to people is that they needed money for the HOTs. And the conversation between Quinn and Sage beforehand seems to indicate that as well. Sage seems unhappy about doing it, and Quinn baits her by saying that Sage could always ask her parents. Sage foreseeably tells her off and says that Quinn would have to tell Tommy about them being unavailable to the DIKs (which she doesn't, leading to that entire drama).
After the party though Quinn tells Tommy that the money was to finance their livestyle, i.e. drugs.
Now which is true?
Option 1: Quinn is lying to Tommy, and the money is actually for the HOTs. Which would be a bit weird, because the HOTs don't usually party with the preps for money, and manage to finance themselves anyway. What made them fall short now? Also it doesn't seem to me that Quinn is lying to Tommy at that time.
Option 2: Quinn is lying to everybody else, including Sage, and the money is for drugs. That would mean that Sage has no clue about the finances of the sorority she is president of, and has handed that over to Quinn completly, without oversight, which seems uncharacteristically irresponsible for Sage.
Now, if Sage was somehow involved in the drug and/or restaurant business, and the money was for that, it would fit a bit better. It would give a better reason for Sage's unhappiness, having to use the entirety of the HOTs to finance something like that, other than just having to interact with her bitch brother. It would also mean that she isn't dumb enough to have no idea about the finances of her sorority.
Admittedly, Sage being in on that stuff would be a huge plot twist, and I don't really believe it. It is more likely to be either questionable writing or a setup for a break between Sage and Quinn, who seem quite close (yay more drama

). But I'm not going to discount the possibility completely.