Hi!
You have picked one of our favorite spots to watch Wishes; just make sure and look up to make sure the wire is running over your head. In fact, you may want to scan the sky above the bridge during the day to know exactly where you'd like to stand.
We often get our Wishes spot anywhere from 15-30 minutes before they begin, but we've had other visits where we walked right to the spot just as they began when we travelled off season. But knowing the importance of this to your daughter, I'd be more cautious and arrive early. You didn't mention her age, but if you bring some age appropriate activities (blowing bubbles, Mad-Libs, coloring, sticker books, etc) to keep the wait enjoyable, the time will go quickly.
When my sons were younger, I would stand behind them and as Tink flew over us, I'd sprinkle them with large pieces of confetti/glitter. They loved thinking Tink had sprinkled pixie dust on them!