Learn to hack. Giving any employee a hazy equity offer with promises to "scale it up" is a bad idea. The better your prospects get the more she is likely to feel screwed. And the worse they get, the less motivating the prospect of continuing seems.

Any scaling equity package should be linked to dates and performance goals. You basically said you didn't want her to own the company unless it succeeded, when success was contingent on her.

Sounds like she trusted you. Then stopped trusting you. Then left a few months later. You screwed up. Go apologize.