Now that I know more about the game I have a list of solutions:

• Switch to peaceful mode to despawn the witch
• Run far enough away to despawn the witch
• Change to creative mode to get invulnerability
• Command give items to yourself to fight back including golden apples
• Build a bedrock wall around her to block her in until you get the weapons you need
• (Optional) Blow her up with lots of TNTs
• Prepare milk before doing

Now that I know more about the game I have a list of solutions:

• Switch to peaceful mode to despawn the witch
• Run far enough away to despawn the witch
• Change to creative mode to get invulnerability
• Command give items to yourself to fight back including golden apples
• Build a wall around her to block her in until you get the weapons you need
• (Optional) Blow her up with lots of TNTs
• Prepare milk before doing

Now that I know more about the game I have a list of solutions:

• Switch to peaceful mode to despawn the witch
• Run far enough away to despawn the witch
• Change to creative mode to get invulnerability
• Command give items to yourself to fight back including golden apples
• Build a wall around her to block her in until you get the weapons you need

The cause of the problem was I was setting the torches too high up to get sufficient light coverage on the ground below.

Now that I know more about the game I have a list of solutions:

• Switch to peaceful mode to despawn the witch
• Run far enough away to despawn the witch
• Change to creative mode to get invulnerability
• Command give items to yourself to fight back including golden apples
• Build a bedrock wall around her to block her in until you get the weapons you need
• (Optional) Blow her up with lots of TNTs
• Prepare milk before doing