If VCC and GND are electrically isolated from Phase, Neutral and Earth, it doesn't matter the direction with which you connect the plug.
Your sensory circuit doesn't even know there's 230 VRMS somewhere else. It will just see the voltage across the current-sense resistor.
Update: It is hard to tell whether your sensory circuit is in fact electrically isolated or not from your mains, because the text in your figure says they are, but the connection between your "mains side" and the GND of your sensory circuit, according to the schematic, says they are not. I have to think that what is right is the schematic, and that you think they are electrically isolated, but they are not. You wrote "This question is not about personal usage risks. Please focus your answers on the circuit level, about the risk on the circuit elements", and I gave you an answer according to that. The one-wire (or two-wire, with little volts between them) connection between the mains and your sensory circuit won't do any harm to your circuitry, and won't distort any reading, but just remember: YOUR SENSORY CIRCUIT DOES NOT SEEM TO BE ELECTRICALLY ISOLATED FROM THE MAINS. If you touch any node of your sensory circuit, you may die. So, be very careful if you have experience with such circuits, and do not build anything if you don't have such experience.
This was one of those crap Chinese-made Mains-to-USB chargers that can be purchased for as little as US$1.50.
I've taken them apart, and they are bad, criminally bad. The isolation from mains to output is not taken seriously- not enough creepage distance, and in one of the samples I examined, there was debris inside that could cause a direct short if you shook the charger just right.
She could have been touching the earphone plug while unplugging or plugging the earphones into the phone, and perhaps a grounded Ethernet port on an otherwise plastic computer. Once you're connected to the mains, any grounded bit of metal can be lethal. Perhaps the computer was metal and grounded.. most laptops these days have a grounded chassis so either the metal, trim, an exposed screw or anything like that would suffice. Whatever the current path, the muscle contractions probably caused her to grip the conductive bits more tightly rather than flinging them away, and sealed her fate.
Best Answer
You don't want your whole house electrical system arbitrarily floating. First, just a tiny leakage or static electricity could charge it up to high voltage. The whole system would have enough capacitance to ground so that the discharge could cause damage.
Then what if any of the three lines were accidentally shorted to ground? You wouldn't know anything happened if one of them got shorted, but suddenly other parts of the system are at lethal voltages.
Here in the US, there is a final transformer near your house, often on a utility pole at the street in front of your house. That makes center tapped 220V from whatever the higher voltage feed on the utility pole is. These are left isolated on the pole and all three lines brought into the house. The center tap is then grounded with a thick cable to a copper pipe that goes into the ground, or to a ground stake just for that purpose. This leaves two phases of 110V with opposite polarity. Most circuits are connected between one of the phases and the center, called the "neutral". A few special high power circuits, like for a clothes dryer or electric range, are connected accross both ends and are therefore 220V instead of the usual 110V.
Part of the reason for the ground setup it to deal with lightening as best as possible. The system is grounded as closely as possible to the breaker panel in the house to minimize the common voltage on the system due to ground offset. Imagine what would happen if the transformer secondary center tap were grounded at the utility pole instead of your house, and there was a nearby lightening strike. There could easily be multiple kV offset between where the center tap ground and the actual ground potential other things in your house might be connected to, like the concrete floor you're standing on in the basement, water pipes, etc. Even well insulated and properly designed appliances aren't going to protect you from that.