While, according to current rules, you are not allowed to have a panel in the bathroom, I don't know when this requirement was introduced. I seem to recall it being in the late 60's.
If my memory is correct, considering the age of the equipment, this very well might be a legal arrangement.

Also please note that ... a bathroom is not a bathroom unless there is a sink in there. If this were a stand-alone shower room, even the current NEC rule would not apply.

One might try to extend switch and receptacle rules to keep the panel outside the actual shower enclosure .... the goal is worthy, but the logic a bit weak.

Let's face it: some things are so basic as to be self-evident, and one seldom sees a rule against them. For example, I'm pretty sure there's no law specifically against stepping in front of a speeding locomotive.
In a situation like this, the 'enforcement' comes in an indirect way, as prospective buyers use this 'improvement' to LOWER the value of the property.