Let's not kid ourselves, she is challenged when hit with "out of the blue" questions, this is not going to be a cakewalk. If she and Joe both come through it without self-destructing, it'll be a tie with little net effect. Both of them have little limited power to score a big gain but can damage his or her own side much more easily.
I think that her capabilities are greatly underestimated. I think she did great with Gibson - he played gotcha and she came right back at him, the byte about the "Bush Doctrine" was spun against her hard. But if you listen she has him flustered, and she answered his question directly unlike nObama ever does.
I also feel that she was forced by her handlers to hold back with Katie and that lead to the uncomfortable "russia" conversation - her full answer with Charlie was actually pretty good, and she's let her frustration get the better of her - that plays fine with "real" people.
So she can't handle trained, professional, and bitter in-the-bag-for-Obama reporters. Big deal. Call it wishful thinking but she knows how to debate tired old crooked politicans - she did it in Alaska.
Joe's going to go into this thinking it is in the bag and he's too arrogant to think she has a chance.
As long as McCain's people don't tell her to hold back I really think she'll nail Biden.
Plus for it to be called a Biden victory he'll really have to destroy her based on the low expectaions the media have set for her.