Grocery Stores & Restaurants have "cheats" to get around FMLA & the law. They don't fire you, they don't lay you off... instead they either "don't put you on the schedule"... or they make your hours as RIDICULOUS as they can under the law. Like a 2 hour shift every 8 hours.
The upside to a large chain is 2 fold :
1) She can kick it to the Union and let them deal with the lawyers and petty politicking (as long as the union isn't in negotiations they should back her) if she's a union worker (crossing my fingers)
2) She can kick it upstairs, and the resultant follow from Crappy McBosserson she can avoid by getting transferred to another store.
My DH lost his job with Kroger for having the gall to not go into/stay at work the day our son was born. Union was in negotiations, so no union support. He'd been an employee and union for over 8 years at that point, and had a stellar record, but a crappy new boss. It's one of the thousands of cases that never gets brought, because we were broke with a VERY new baby, and couldn't afford to waste the time or money. Turned out for the best, because he ended up getting a great job that paid 10k more per year, and it had a REAL schedule, so he could go back to school, which turned around and really upped our income level... but at the time it was super stressful.
If her boss is being a real jerk, he can certainly make her situation impossible. So try and kick it up the food chain... but just be ready. Either way, she wouldn't have a job... so there is no harm in trying.