You are right Grog. She flies from the top of the Matterhorn to the top? (or by) of the castle during the fireworks.
You can watch from almost anywhere. In front of the castle is way too crowded. I suggest behind the castle in Fantasyland, or on the balcony on Innoventions, if they still let you do that. You can also see from DTD & inbetween DL & DCA, but there is no music.
There is a point @ the end of the fireworks that is all gold & seems like the end. It's not, more will start up again & the finale is all silver. Many people will leave @ that point thinking it's the end, stay until the silver fireworks.