Uh, Why Is Sen. Feinstein Afraid To Debate Her GOP Opponent, Elizabeth Emken?

Yeah, I do not get why Sen. DiFi is afraid to debate her very little known Republican opponent, Elizabeth Emken.
But here is our illustrious senior senator in action.
While an actual reporter, from a San Francisco television station no less, asks what I think are reasonable and legitimate questions about why Sen. DiFi, as she is affectionately known here, won't even consider debating Mrs. Emken.
So, here is KGO television's Mark Matthews and what he was asking Sen. DiFi:

Matthews: I got to ask you about Elizabeth Emken. She wants to debate you. The L.A. Times came out and said you ought to debate her.
Feinstein: I’m running my own campaign.
Matthews: Is there anything more you can add to that?
Feinstein: I did a large event in Modesto, did three or four meetings, I’ve been to Southern California’s and that’s what I’ll continue to do.
Matthews: Wouldn’t it be better for the voters to hear both sides?
Feinstein: Thank you very much.

Yup, that is all she wrote. Thank you very much and Sen. DiFi walks out. At the Democrat National Convention no less.
And here is the funny thing.
Of all newspapers in California, the Left Angeles Times is asking the same thing.
Granted, this is an editorial from July 17, 2012. But the point is that the Times wrote what is the obvious:

Nothing screams "entrenched incumbent" more than a refusal to debate an opponent.

Exactly.
Maybe it is because they are not all that certain that they have this election in the bag.
There is this poll that the Emken campaign is touting that seems to indicate she is closing a gap. However, there are 20% of voters according to this poll that are undecided. That seems awfully high at this point in the election. Especially when you look at the presidential number.
OK, say the 20% is because no one knows who Mrs. Emken is. That is possible. And she roughly maxes out at 34%. What I mean by that is that if one looks at the Republican registration in California, about 31%, then she is over that. So, if the 20% is true, or even close, then she may have a shot. And if the poll is right about Sen. DiFi, that she only has the allegiance of 46% of those polled, then maybe she really is in more trouble and is not willing to give Mrs. Emken the time of day.
But here is the thing.
Even a Republican that has no chance of winning can get at least 35% of the vote in a senate campaign. So at best for Sen. DiFi, Mrs. Emken is almost at her ceiling.
Or is she?
Is there something in internal polling that Sen.DiFi is worried about? Is it that Mrs. Emken is gaining ground? Is Sen. DiFi losing ground?
No one really knows for sure.
But it would do Sen. DiFi some good to actually debate Mrs. Emken at least once. Because all Mrs. Emken has to do is repeat this from the Left Angeles Times:

Nothing screams "entrenched incumbent" more than a refusal to debate an opponent.