Can my daughter's 40hr week job force her to have open availability? She has a doctor's note that she's her father's caregiver.

Ok my younger daughter is my husbands caregiver He goes to daycare 5 days a week and gets home around 5pm. My daughter works a full time job same job for quite a while and has given them a Drs note stating she is his caregiver and must be home by 6 to take care of him. Today she was told they can no ;longer accept this and we all have problems at home and she must change her availability to work till 9 when the they need her to. Right now for a while she has given them one nite a week till 9 and now this. She also just got another position with better hrs in same place and now they want to change that. Is there any help to get with this as she cannot afford to lose her job but wants and needs to help her Dad She also has a 3year old son that we watch for them . Where can we turn or is there an attorney or someone to help us. This just isnt fair as he deal so well with her Now what another change for him This is so unreal Please help if you can We live in NJ