Family caregiver letter to HR department for niece's job?

This should come from a doctor, not from a family member.

I’m not sure I understand. A full-time caregiver is usually “on-site” 24/7 and does not work a full-time job. Plus you say she also “works in the evening”. They also have In-home Hospice Care. I may be misunderstanding what you’re asking, but to me, I sounds like all she does is sleep there and maybe be on-call during the nighttime hours.

You need to find out who they need a letter from and why. Is she applying for FMLA leave? Do you have POA? The letter may not hold any weight unless you are representing them in some official capacity. You may need to get a letter from the Hospice agency saying that your niece is taking part in their care, or will be if she’s granted that leave if that’s what she’s asking for.