How to erase data from an unresponsive iPhone

What did you end up doing? I am in a similar situation but not selling passing phone on. trying to discard it 'securely' and correctly.

Worst-case scenarios are running thorough my head LOL If someone manages to turn it on (not even trying to get online which is when all data will be erased by my pending erase), what could they get their hands on?

If your iPhone is dead and Find My was not enabled then there is nothing that can be done now. If you have a backup then all your data can be restored on your new device. Else all your data is also lost. You need to start afresh with your new iPhone.

If you have either dropped the device accidentally or exposed it to liquid or used it beyond acceptable temperature limits then…

Take your device to an Apple Retail Store or Apple Authorized Service Provider, or contact Apple Support:

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Contact Apple for support and service - Apple Support 

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Contact Genius Bar.

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I'm sorry to hear about the issue with your daughter's phone. If the phone is completely unusable and offline, it's unlikely that it will magically come back to life. In such cases, the best course of action is to take precautions to protect your daughter's data.

Changing the Apple ID password was a good step to secure her account. Additionally, you can follow these recommendations:

1. Contact Apple Support: Reach out to Apple Support directly and explain the situation. They may be able to provide further guidance or assistance in remotely erasing the device from their end.
2. Remote wipe when the phone comes back online: Keep the device listed on Find My iPhone/iCloud. Once the new phone arrives and is set up, if the old phone ever comes back online, you can initiate a remote wipe to erase all data. This way, if the phone does become functional again in the future, it will automatically erase itself.
3. Remove personal information: Before considering deleting the device from Find My iPhone/iCloud, make sure to remove any sensitive or personal information associated with the device. This could include contacts, photos, documents, messages, and any other personal data stored on the device.
4. Securely dispose of the device: If the phone is irreparable, you may want to consider physically destroying it or recycling it through a reputable electronics recycling program to ensure that no one can access the data on the device.

It's always better to err on the side of caution when it comes to protecting personal information. If you have any further concerns, it's advisable to consult with Apple Support directly for specific guidance based on your situation.