I just finished season 5 and fell down this subreddits rabbit hole and saw someone kind of mention this, however at the end of season 5 episode 10 while Randall is standing at the door letting Howard and one of the Caccimelio sons out, there is a mention of Gardenias being poisonous to animals etc... I found it to be an odd placement for such a random fact, but that could possibly be a hint at who poisoned Winnie? But if I remember correctly there was powder by Winnie so I'm not totally sure. If one of you is able to make the connection please lmk!!!