Just an edit to this as there is a mistake with your description of they/you. Capitalized "Sie sprechen" is only "you speak" (formal you, singular or plural). Non-capitalized "sie sprechen" is "they speak". Non-capitalized "sie spricht" is "she speaks". If it is the start of a sentence (meaning it is capitalized "Sie" regardless of who it is) then you would need context to tell if it is "Sie sprechen" (you) or "Sie sprechen" (they). If I've confused people more, maybe the chart on this page will help? If it doesn't help, tell me to shut up and go away. ;-) http://german.about.com/library/anfang/blanfang02.htm
I'm sorry if I'm asking a stupid question, but why is Waruber used instead of Was? Is is a matter of personal usage or are you forced to use Waruber here? If preference, is there a tendency for waruber to be used in one region more than another... and if a requirement, what is the difference? I'm scratching my head pretty hard. Thank you for any input.
When I hovered over Waruber it came up as "what about" as apposed to just "what", for instance I imagine you would also use Waruber if you were to says "what is he worrying about?" whereas "Was" seems to be when something is, e.g what is that = Was ist das. I think that's right but I'm not sure and I hope that makes sense :)
Not completely sure about this but, "what is she saying?" is asking for what she literally said whereas the translation of "what is she talking about" asks about what she is saying more generally.
For example: A woman says, "For breakfast, I had a bagel".
A response to "What is she saying?" would probably be something like, "She said she had a bagel for breakfast".
A response to "What is she talking about?" could be, "She is talking about what she had for breakfast".
You use 'spricht' in case of third person singular (er/sie/es), and in case of second person plural (ihr-you all) it is 'sprecht'. http://german.about.com/library/verbs/blverb_sprechen.htm
Do not end English sentences with "about". About what is she speaking is correct, although it has now become very unpopular due to misuse of incorrectly ending sentences. If DL marks my German wrong because I mess up nouns/verbs/nicht at the end of sentences, then they should make sure the English is spot-on correct. Danke.
The questions are slightly different.
"Is that all she talks about?" asks whether she only has one subject that she talks about, ever - and probably implies that she doesn't seem to ever talk about anything but that one subject.
"What is she talking about?" asks only what she is talking about now - not whether that's the only thing she talks about ever.