The only likely way that could happen is if the transformer (the white charging block) was plugged into an extension cord, and the end of the extension cord also fell into the water.
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Yup. That, or she reached up, while in the tub, to plug the iPhone cable into the charging cube while it was plugged into the wall.
Immersed in a tub of water, you are most definitely seriously grounded and highly vulnerable to being killed by the voltage from a standard wall outlet (120 v at 15 amps).
Standing on a wood floor, or wearing rubber sole shoes makes you far less likely to be killed if you touch an electrical outlet. Your are ungrounded in this condition. Much like birds can land on ultra-high volt transmission lines without being killed as the electricity can’t travel to ground. Now if the bird tried to straddle two wires with alternating potentials at the same time, then *poof*. Instant fried chicken.
Half a century ago while working in communications in the Army, my coworkers and I were not required to wear our metal dogtags or the chain holding them. If you are working above an operating piece of equipment to repair it, the tags can suddenly fall out of your shirt and into the equipment, providing an excellent path for electrocution. Rubber soled shoes are very helpful but not sufficient.
It was also standard practice to work with only one hand. The other hand would be firmly in one's pants pocket. This would reduce greatly the chances that a deadly current could flow from arm to arm, stopping the heart.
I can remember frequently finding that my pocketed hand would ache at the end of the day from being in the pocket.
Another thing worth noting is that the marketplace, including china, is more than willing to supply sub-standard USB charging devices that presented both a fire hazard and an electrocution hazard. The typical USB charger uses an isolation transformer which should prevent the AC from appearing on the output of the device and the rest of the charger circuit uses optical isolators to prevent dangerous failures. Unfortunately, the sub-standard chargers allowed metal connections to be too close for long-term reliable operation. I know this because I bought some chargers before checking them out sufficiently. I never used them.