You are told not to open the radiator cap not because of the car (if the radiator has overheated then most likely the damage is already done) but to protect yourself from being scalded.
If you really had to open a boiling radiator you would do it by putting a heavy cloth over the cap, turn it and quickly run away. You will hear "phshhhht" and then the water will spray everywhere. Idea is to deflect the hot water downwards rather than up all over you.
Sounds like a good idea for her to remove more than 1 article of clothing
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