A predictor can vote in line with her prediction, but:

• if she controls a majority of all reputation in the DAO then… she’s the DAO and it’s not an attack.
• if she doesn’t control significant portion of all reputation in the DAO but does control significant portion of the voting reputation over this proposal (since overall voting reputation is still low, as we expect it to be), then by manipulating the voting result to “her side” she’ll create the incentive for those who staked oppositely (and risk losing their stake) to alert the DAO and its voters that the voting result seem “non-representative” (it is “under attack”), who’ll then encourage more voters to participate in the vote in order to reach a representative result.
• if she doesn’t control even significant portion of voting reputation over this proposal then… it won’t matter.