Before turning his nose up at the AB offer, OP should do the research to make certain that his mother is entitled to the EU 261/2004 compensation. If she's not, she gets Eur 0 under the rule and nothing from the customer service gesture offer.
Some things are clear, e.g., weather or ATC delays are likely outside the carrier's responsibility while technical issues are likely within its responsibility. But, there has been a good deal of writing recently suggesting that carriers are not paying compensation and are prevailing on technical faults when the part in question had been properly installed, was within its tolerance period (it' supposed to last 1,000 flying hours and it's only been 250) and it nonetheless fails although inspected.
All of this a long way of saying that there are far too few facts in the OP to determine what OP's likelihood of success might be.