Discover and change ownership of IOS Apps

My wife phoned me in a panic when her WhatsApp stopped working and demanded a password.

NOTE 1: This demand does NOT specify WHICH password (e.g. which account) is demanded

Numerous tries using her usual Apple ID fail. She then uses the default solution which is to contact me (I am currently in a different country)

She wonders if the app is owned by me, not her

NOTE 2: I do not own a smartphone, and WhatsApp does not work on an ipad so I have never downloaded this nor considered using (on any device). I have never used any of her iPhones (apart from debugging crises like these)

I try everything I can think of and spend ages on google trying to learn what Apps I "own". I fail.

I cannot find any way to change ownership, presuming I knew in the first place. I have found comments to the effect that it is impossible to change the app ownership once it has been downloaded, and that the 'solution' is to delete the App and redownload with the correct Apple ID

This is not a welcome solution as deleting the WhatsApp app will lose all her years of messages, etc. Non-starter.

My questions:

1/ Why is the ownership of an App considered a secret and is not visible?

2/ related to this, and in common with MOST of Apple security, when I get a password demand, why do you consistently fail to indicate WHAT you are demanding access to. e.g. "Please provide the password for Apple ID fred@flintstone.com"

3/ Why is there no mechanism to transfer ownership -- especially for free to own apps, but also could demand payment prior to t/f. This strikes me as development laziness.

I am a IT security expert. When weighing up the relative security concerns of:

a- providing vital information like the Apple ID used (which gives a tiny but essentially useless clue to the hacker, especially given the other security measures such as strong passwords and checks for unusual activity)

vs

b- forcing me to communicate my Apple ID password over unsecure channels so that my wife can continue her life

there is no question in my experience that option (a) is far more secure

Apple is obsessed with security which they implement in haphazard, inconsistent and confusing fashions which inevitably promote insecure practices from naive users, thus undermining the original security intents.

(for example NO professional I know uses the dreaded '2 factor authentication' and this introduces far more security holes than it fixes)

Please at least fix this one and let us manage our apps