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This is very interesting, but I found it a bit hard to follow. If you spaced it out and added something more, it would be better.

Overall, it's very good and I definetely would be interested in reading more.

Well you should add a few more lines of description to it and maybe make it a little easier to read.
Its hard to feel for either of the characters. Whey? Because I don't know what they look like...

Very gripping, and quite startling.
I really like the way you've distanced the reader from the scene, which has more effect than being inside the characters head. It's a hard trick to pull off, nice work.
It's a great scene, but I agree that you could add more detail to the room and danielle, before you move on to the action. Also, at the end she continues to play the piano, but the room is silent. I'm not entirely sure if that works.
Keep up the good work. Kudos.

firstly,

i think you missed out the word 'of' in between smell and lilac in the first line.


you say the room is peaceful and serene and then you say someone is whimpering.
maybe you could say the room was peaceful and serene until danielle heard the whimpering in the corner. she missed a note and sighed.

“I said stop it!” she whacked the woman over the head repeatedly screaming “shut up” the entire time.

Interesting as an opening - the successful prologue is the one which makes the reader curious as to what follows, and at the moment, I'm dying to know what happens next. Though, on the note a prologue, it might serve you better to include the title of the complete story in your subject line: "Prologue: [Insert Title]"...

Some suggestions:

Grammatically


[Green is used for corrections, Blue for comments].

It was a lovely day; the living room was filled with the smells ['smell' has an unpleasant conotation to it - perhaps 'scents'?] of lilacs and daisies. Danielle was sitting at the piano, facing the open window, feeling the breeze in her hair. The room was peaceful and serene[s],[/s] and [possibly cross out 'and' and write 'until'?] suddenly Danielle missed a note. She gave a sigh [what kind of sigh? calm? annoyed? short? slow?] and turned to the whimpering in the corner. “Stop your crying[s].[/s] ,” Danielle whispered, but the whimpering continued[s];[/s]. Danielle grabbed the bridge of her nose and got up. She walked over to the corner and grabbed [two 'grab's within the space of two sentences; I would find a difference word] the marble candlestick holder. “I said stop it!” [s]s[/s]She whacked the woman over the head, repeatedly screaming “shut up” the entire time. The lady’s groans and gasp[s]ed[/s]s soon stopped, and Danielle walked calmly back to the piano with a [s]slight[/s] [superfluous adjective] splatter of blood across her daffodil-colored dress. She began to play once more, and the room fell silent.