She is building a social network for hobbyist gardeners. Apparently this is what humanity needs more than geek toys like self-driving cars and augmented reality sunglasses.
Additionally, I think many people would consider Facebook more valuable than augmented reality sunglasses. If we're going to only build things that humanity "needs", we're going to needlessly limit our scope and put many people out of jobs. After all, our needs are considerably less than our wants.