The reason is that Cass's Tears is almost a non-power... and by that, I don't mean a Stunt. I mean, it's a player-owned, GM-controlled plot device, not a power.
If you want your player to have something like that, then great. [-0] is fair for that, and retool it however you feel... but it hardly needs to be part of an item at that point, and definitely not worth the debate I see coming... ("But it's a free power!" -> "But because you put it in an IoP, it costs more! RAWr!" -> "But if it's in an IoP, I can lose it, etc!" -> "Yes, and that loss of utility and function will cost you more... cause... cause it does!" -> "If anything, it should be worth less! Sort of!")
For what you're describing, I'd go with a Cass's Tears reflavor to the effect of replacing the "and no one ever believes me" clause with a "worse, I always seem to be right." Pessimistic, mystically self-fulfilling prophecies.
If you want anything past that- anything that affects stats, or game-play in the moment, rather than in the plot... you have some good recommendations for powers or stunts... just make sure that the grand total cost of your IoP is 1 or better... because at that point, it's actually useful and should be paid for, per IoP minimums... come up with at least [-2] worth of powers and/or stunts you like, tack them and the Cass's Tears reflavor onto your IoP (with +1 refund if it's discreet), and not only do you have a ring that makes you paranoid and tragically right... it also prepares you in some way for that worst-case-scenario you saw coming (or didn't).