I don't know her medical history, but not passing water for 3 days is a danger sign.
Is she producing urine and not passing it OR is she not producing urine?
If she is not in abdominal discomfort and hasn't passed urine by tomorrow morning, then call the on call GP
I presume she hasn't got a catheter in situ.
it's been nearly 72 hrs though.
Besides, getting hold of someone takes time.
I am usually a "don't contact the NHS" person BUT on this occasion i think it's important (and urgent)