What are you basing this off of? She damn sure wasn't a killer in these last primary debates.
The only debate where she stood out was the one where she was grandstanding to call Biden out on his busing views, and we literally found out the next day that she agreed with him and had timed a T-shirt release in the least authentic manner possible.
Also, let's not forget that Tulsi fukking Gabbard (literally the least popular Democrat in contention towards the end) took her soul on stage and had her stammering and looking awkward. I'm not so sure what we've seen so far that tells us she's so formidable a debater.