Can I play as Cadence beyond the tutorial?

You can play as Cadence after the tutorial as soon as she joins your group. Before she joins your group, you will encounter her in several caves where she grants you some special technique or a key item.

When you encounter her for the fourth time, she will join your group.

Although the map is random, the cave locations aren't:

• Lake Hylia (lower right corner)
• Gerudo Desert (look for the red banner)
  
• Death Mountain (Near the Entry to the large area of the Tempel of Storm)
• Lost woods (Right at the entry of the woods)

The cave next to Link's house does not count, though. It only provides the initial shovel and torch for Link and is empty if you start with Zelda.