I mean there are only two real possibilities when she says "I have a plan for the energy crisis but I can't tell you until next week if I win".
1) You don't really have a plan, you're winging it and hoping something turns up
2) You do have a plan, but it's awful and you can't afford to reveal it before it's too late and you're already in post
Both awful looks, I mean it doesn't even matter now because voting is essentially done. The result is tomorrow. Whatever you say one day before then will make no difference to the result.
Mind you Cameron won an election with a pledge of "we're going to cut billions off the welfare bill, tune in after the results (if we've won) to see who exactly we're chucking into a massive hole for no reason". Then people on tax credits and the like who'd voted for them started wailing on that oh no, I didn't think it was my benefits you'd take. Just those of the awful scroungers of whom there are er, statistically basically none. Well fuck you, don't vote for people like that.