Is it going to be a problem for us if our home caregiver is illegal?

Just found out that the homecare person we got for 12 hour night shifts is not a citizen . She works for an agency that employs predominately Polish women. The caregiver is wonderful but I suspected that she was not on the complete up and up when she acted cagey about days off. I mean isn't it against the law to work 3 weeks straight 7 days a week with no day off? I'm just hoping my mom doesn't get in trouble or will the agency just take the fall if she gets caught?