If the tub is damaged and repaired per the homeowner's request, then it sounds like the tub SHOULD be replace; not repaired (because it's temporary.)
If something heavy or sharp was dropped on the repair, the repair will deteriorate at a much higher rate than original work because, well, the repair is not 'original workmanship'. The 'cause' of the damage is the only 'part' of this example that is the same. (What happens once the damage is done, happens at different rates. Remember, based on your example, the 'cause' of the damage is the same.)
People should ask how long that person has been in business.
And that person might not have properly made the repair. That's why we hire experts. As a consumer, at some point along the way, we have to give the contractor some credit that he knows what he's doing, or we find someone else. Even reputable contractors end up in court, or out of business. (This point is moot, IMO, because the good-guys and bad-guys don't always make proper repairs.)
If one was to take care of a repaired tub, like taking care of an automobile, it will last a long time. I don't know what one has to do to 'take care' of a bath tub. It's not like there are 'parts' that need regular cleaning or replacement. On a car, sure, one should wash and wax the body on a regular basis, and one shouldn't wait until the car is 10 years old to start washing and waxing it. But, for the most part, cars (and tubs) these days don't need much cleaning and waxing (on a general basis) to preserve them. So I'm not sure what it means to 'take care' of a tub. (I've got the feeling that it means more than cleaning it every week or so with Scrubbing Bubbles.)
I certainly commend you on you and your Father's experience in this trade. (Truely, there are damn few good pros out there.) At the same time, as far as "that young lady's story not being there", fact: the repair lasted 2 years, fact: what would it cost to 'undo' the existing repair to 'do the job right' (as you imply), fact: the contractor is out-of-business.
After reading the facts that we know, if another repair was attempted, what would it cost? Would a 2nd repair last as long as a 'first repair'? Could a 2nd repair even be performed? A pro would have to come in to review the situation. She wants to do this job herself. Would you recommend she do the job herself? I figure that if she's gonna spend good money on another repair (and I'm sure that your work is not 'cheap'), she ought to consider getting a new tub/stall. And if a new stall is TWICE the price of a last repair (that you can perform and warrant), it may be worth her time to get a new one. I guess that's what I'm saying.
I apologize if I'm implying that you are a 'bad' contractor. Quite the contrary. Your suggestions are valid but I must add that the option of getting a new tub is worth considering. 'nough said.