That's why she'd find it by accident. She's not looking for it specifically, she's looking for weed, and maybe she'll confront Quinn about it or maybe she'll take it, or maybe both.
Oh brother.
Well, we had something like that in Ep 5 when choosing between Josy and Maya. Could happen here too. I mean, Sage doesn't strike me as a threesome or foursome kinda gal. She doesn't even strike me as a gal interested in other gals either.
I wouldn't think that she'd die, just OD, and I don't see it as being something unbelievable, in fact it feels exactly like something you'd see in a movie or TV show.
Let's say that things continue to go badly for Quinn and the walls are really closing in around her, and since Riona is basically like her closest ally in all this, Riona's feeling this too. We already saw in Ep 3 that she seems to be stressing out and in Ep 4 she's developing some paranoia thinking she's possibly being followed. It's possible that this pressure starts to get too much for her and she looks for a release, so she goes to have a smoke but finds she's all out so she goes to see if Quinn has a stash and finds the bag.
From here, it can go one of 2 ways; either she confronts Quinn about it and says she's going to get rid of the bag, or she just takes the bag to her room. In the first scenario, it could be one of those cliche moments where she's going to flush it down the toilet but changes her mind because she still feels like she needs to take the edge off her stress somehow. In both this and the 2nd scenario, she takes it to her room and snorts some of it. Since she's never had it before she could have a bad reaction, or maybe it's laced with something else and that's what causes her OD.
Either way, this is something that not only feels like it would be pulled right out of a TV show plot, but it's something that I feel does actually fit with this game.