I thought I read somewhere that the FFCRA applies to household employers. So I think you’re still on the hook for paying 2 weeks salary at full price and 10 weeks at the 2/3 up to $200 per day rate, but this is offset by a federal tax credit (assuming you’re paying on the books and legally).

As far as liability from a tort standpoint, like others said, I think there’d have to be negligence (e.g. you had her come over knowing you had exposure or are positive). Or maybe if you lie about something such as saying you’re social distancing, but then she can prove you caught it from attending a large social event (hard to prove, but this is theoretical). Otherwise if everyone (nanny and family) catch it around the same time, I think it’s hard to prove who infected whom.