I fail to see what is so outrageous about her prediction. Let me repeat the quotes from the summary:
"I think we're going to have strong indications of life beyond Earth within a decade, and I think we're going to have definitive evidence within 20 to 30 years.
Is that really so implausible? There are hints that there is or has been life beyond Earth even in our own planetary system. There is solid evidence for many planets beyond our solar system, and although these discovered planets are usually too large to carry life similar to our own, they strongly hint that there are also smaller planets out there that could carry such life. Yes, Ellen Stofan is speculating, but if she's asked to speculate about the subject, this seems to me like a pretty solid reply.
We know where to look. We know how to look. In most cases we have the technology, and we're on a path to implementing it."
Again, pretty solid reasoning. What's the problem?
Of course she can still be wrong. Predicting the future is hard, and there are no perfect guarantees, but her prediction sounds pretty plausible to me.