Nope. Absolutely not sure. Tell me what you think when you see her clothing. It doesn't look like our usual Donna fare -- nor does the (apparently) short hair. It looks like something from ... somewhere else. The end of the universe comes to mind, actually, with that coat. So, is she alt!Donna or Donna from a different episode under very different circumstances? No idea. Alt!Donna is the guess since Rose is coming back, but it could be anything.

I just heard a radio interview with Tennant in which he was asked "Has Catherine Tate signed for another season?" He dodged the question neatly by saying that "Donna has quite a story arc during the remaining episodes of this season." (paraphrased)

*needs more Donna icons*