At five mana, she's more comparable to Venser I think. She can marginally protect herself without anything else on the board but he's harder to chip down going +2, naturally hits his ult a turn faster and his emblem is more gamebreaking (though either should win you the game). Of course he's much stronger with his toys to play with. She might be a maindeck 1-of in Delver/Spirits or whatever though, just because she can end up being a Tidings or whatever, might replace Jace as a board card in control mirrors since she can continue exerting a mana advantage by tapping their land down. Usable but no more than a fringe player most likely.
