How do I make an ore kill someone when they touch it?

Depends on the ore. But assuming we are talking vanilla minecraft:

Redstone ore has the interesting property that is emits a signal when steped on or otherwise interacted with. So you could simply place a command block right next to it and have that execute whoever you want killed.

You can do that by downloading the Fake Ores mod, which you can download at Curseforge.

This mod will add fake ores in your Minecraft world. When you break a fake ore, it becomes alive and then attacks you. All fake ores may drops some items that allows you to craft the Ores Boss spawner. A cup spawn when you kill the Ores Boss.

You could detect if she had any of the "bad" ore in her inventory via the following command.

/clear playername ore_name -1 0

Replace playernamr with your friend's name and "ore_name" with the name of the bad ore (coal, redstone, iron_ore, etc.)

Put that command into a repeating-aways-on command block leading into a chain-conditional-always-on command_block with this command

/kill playername

This will make it so that if the first command completes successfully, the second command is run, killing the player.