Sadly this is not unheard of. In a lot of companies, where early retirement is an option, the final figure given is based on final salary so hours may be cut etc to reduce payout. In addition, such an extreme change in work hours can be foisted on a person at a low ebb to 'encourage' hem to leave with little entitlements.
So, what to do next? Some thoughts, for what they're worth. This is form someone who spent some years as a shop-steward and is now management, so i can possibly help show both sides?
Firstly, it cannot be understated that acceptance of these changes without dispute is seen as acceptance of changes to contract, whether written or not. Therefore she should not accept them!
Secondly, she needs at this stage to involve her union. This will need back up and help - she'll be fighting a losing battle alone. The union will fund a lawyer if needs be.
3rd - She should always be aware that if she leaves, the award of most courts where a claim of constructive dismissal is brought - where the employer makes it impossible for an employee to stay but doesn't fire them, they leave to save their sanity and/or health - is almost always a pittance compared to salary.
4th - it may be unavoidable, so can she actually work these hours? It may put her out, but could she walk away from a job after 22 years so near to retirement?
5th - she needs to speak with her HR manager. This should be done with her union rep in the office. Outline the fears that she has and point out that she has a contract and will not be happy to change it after such a long time.
It may well be that a letter from her doctor regarding stress (mention the UK's Health & Safety Act 1974) and the recent bereavement may help her case, as might a call from your good self. It may not...!