Yeah, I noticed that last week. My guess is that she's just filling in for Mark Riley/Tim Lester while they're on holidays, although I definitely think Nat could make it in a major metro market if she really wanted to!
To be quite honest, I'm not sure why Daniel Gibson was appointed to be a newsreader of the 6.30pm bulletin. It's also quite odd how he still presents Weather Updates in non-bulletin regions.
In any case, the presenter isn't the main problem with Prime7 News at 6.30pm. How about showing some of those reports from Kathleen Curry (Prime7 Sydney reporter, mainly covers general NSW politics perhaps with some sort of generic regional flavour) during the 6.30pm rather than the local bulletins? That way, the 6.30pm bulletin might look just a little less like a condensed and Prime7-ised Seven News Sydney!