Stories that hinge on a lie

So I'm writing a story at the moment that involves a young girl finding some portal to a magical universe that fulfills nearly every single childhood fantasy she has. An evil corporate trillionaire tries to take over this universe, and while she tries to protect it, she also lies to the inhabitants of this universe that nothing was coming after them at the moment; in fear that if she did, they were going to shut the portal off to her.

The way I'm writing it at the moment, the whole story seems to hinge on a lie, and while it's not the cliched 'liar revealed' plot I'm still not sure if a conflict like this would work particularly strong. Sure, I coupled it with the fact that she's trying to singlehandedly stop the villain in order to let her lie get invalidated, but I don't know if past uses of this are even effective.

I would say that I root for the bad guy here. Magic from that universe would turn Earth into a frigging utopia.

Anyways, I don't think that lie of her is going to last the entire story. She's alone, and she needs help.