I have seen her referred to as both over the years - Twilight and Starflower - but more commonly called Twilight [I always assumed due to colours and the presence of stars]. I tend to go by what the symbol is rather than the body/hair colour [as other wise we would need to rename a lot of ponies which have variations in colour but not in symbol] so for me, and I am sure for others, she is more supposed to be a Starflower rather than a Twilight.
She came with the Mexican Poof & Puff Palace. I dont think she was named on the packaging or even in the box - I am sure she was just included as a surprise pony. But I could be wrong, perhaps she was named on the box as Twilight or some incarnation of that name and that is part of the confusion?