In reply to owlart:
If she wants to fight it, talk to ACAS, CAB or a union (you don't need to be a member for most of them).
https://www.gov.uk/training-study-work-your-rights
https://www.gov.uk/maximum-weekly-working-hours
It sounds like the employer is being an arse, so will probably try & manouvre her out if she does protest too much.
Personally, I'd ask why I had to do it in my own time (maybe the employer can't allocate the time..in which case they're incompetent or lazy!). Then ask to be paid for it (perhaps gradually) or for time off in lieu.
If all these were refused, i'd do it and then slack off as much as humanely possible. I'd also be tempted to drop a few teacups (prefereably on the bosses car)