I'm not getting why ya'll are calling this card insane. Three mana is not a reliable turn 1 play for Vintage. It's mid-range territory. Think Tinker, Monastery Mentor, or Yawgmoth's Will. It' s a fine card, but I don't think it plays the same role as other white hatebears play.
What it does, and quite well, is allow existing creatures to deal a finishing blow. It stops blockers, including mentor tokens, from doing anything the turn they arrive. She also has a twisted form of "haste" since anything arriving after her won't be able to block her that turn. I can see someone dropping it on turn 4 and threatening lethal on the next swing between this and a Thought-Knot Seer; that's 7 damage right there. Pair it up with something hasty next turn and you're really swinging for the fences.
As far as mana denial goes, I think she's quite a bit worse that Root Maze. Not hitting basics is huge; Gush can still usually get value and fetchlands don't get turned off twice if the controller has a basic to fetch.
In the age of Lodestone Golem, 3 power with first strike was a big deal. In a world of Mentor and Eldrazi, I'm not sure it really cuts the mustard anymore. I guess it does present a pretty big wall against any creatures that incidentally deal damage, like Dark Confidant or other hatebears.
I think -- I might be wrong here -- the only 3 casting cost white hatebear that sees play is Vryn Wingmate, right? And, that card has evasion and an ability that stacks better with all the 2 drop taxing effects.
Overall, card seems totally fine and a role player. Probably playable, totally worth picking up a set. But.. not super amazing. I'd have been more excited if this was a 2/2 for 1W with these abilities.
Anyway leaving Vintage playability behind and, moving on to the casual / fun category: Card is AWESOME there! I'll be brewing with this little lady in Stasis. A playable, one-sided root maze is just what that silly little best-artwork-ever card needs to really take off!