Ivy is generally good friend for Lena if you accept her motives, as she describes them, as true -- she has Lena's back (she won't tell Axel where Lena lives, e.g. because Lena has asked her not to), offers Lena advice which she thinks is the best in her situation (the actual quality of said advice is debatable, but it fits Ivy's personality and beliefs) She respects Lena's choices -- she won't try to push again drugs on Lena who refused them once. She respects Lena's decisions, too -- it'd be very easy for Ivy to wreck Lena/Ian relationship e.g., simply by revealing to Ian that Lena fucked Axel. But she keeps Lena's secret instead, despite your belief she hates seeing these two together.
While i agree that the writing does leave possibility of Ivy acting suspiciously, this is, like you note yourself, only a possibility with the alternative that Ivy isn't actually a bad actor. As such, i disagree with the statement that Ivy isn't a good person "whichever way to slice it" -- it requires slicing it in certain way to view Ivy as a bad person. If you slice it the other way, treating what Ivy states to be her motives as truth, then she can absolutely be viewed as a decent person.