Fired for a medical reason

Posting for my daughter. She has struggled for years with mental health issues, and it's been especially bad for the last month because her meds changed. She's been with a company (restaurant) for three months and reached out to her managers, explained her medical condition, and said she was looking at a partial program that ran from 8-3 so she'd still be able to work her regular shifts. After one day, she realized doing partial and getting to work was too much, and rather than miss work, be late, or call out, she unfortunately elected to stop partial. A week later, she made an attempt on her life and was admitted to an inpatient program for the next 7-14 days. While at the ER, waiting to be admitted, she texted her manager and explained that she was being admitted, and apologized that her shifts would need to be covered. They replied back, "I think it's best we part ways." I TOTALLY get that covering her shift and her as a server, her employment is very tenuous, even on the best of days...BUT given this was a medical condition, was this legal? We are in PA, which is an at-will state, so I don't hold much hope. She's very devastated, and it's only adding to her stress in the hospital--knowing she's getting out and unemployed. I'm not entirely sure what I'm asking from the group here... was it legal for them to fire her? Is there any point in pursuing it when she is released? And honestly--managers, can we not have a bit of empathy for people dealing with chronic illnesses? Would it not have hurt to just reply, "We're so sorry you're ill. Please focus on getting better."