Nora Jansen is an "impossibly stylish and cool lesbian" (1.15) who asks Piper out for a drink and slowly draws her into a tangled web of drugs and money laundering with her "wit and charm" (1.26). While in Bali, she convinces Piper to jump off a waterfall, and later tells her that there's no way she'd have jumped herself if Piper hadn't gone first. To Piper, this is the moment where she "should have understood that Nora was not to be trusted" (1.55). Yes, because the whole drug-dealing thing is so trustworthy.
Many years after Piper leaves Nora and the drug biz behind, Nora and Piper (and Nora's sister, Hester, who's also in the drug trade) find themselves in the same prison together. In the same cell. Piper says, "our troubled history was suddenly matched by our more immediate shared experience as prisoners on an exhausting journey" (17.93), which is a lot of words to say that they make a temporary truce while they're in the same 12x12 space.
Nora swears that she told the feds Piper didn't know anything, though Piper says, "her story was plausible, but it could easily be a lie" (17.115). Whichever it is, she feels bad, and that's good enough for Piper to forgive her… you know, at least while they're sharing the same cell.