The Face ID hardware component is directly attached to the display of an iPhone. This what could have happened:
She went to a third party repair shop and the technician accidentally damaged the connectors for the display, causing Face ID to fail.
The infared camera, dot projector, and/or other sensors that make Face ID work are also fogged up due to the showering, which would likely be costly even if done through a third party shop.
She had the display replaced along with the front camera, which not even an official Apple repair can remedy as every display is paired with the security module of the iPhone’s processor during the original manufacturing process.