How long before someone is diagnosed with Shingles are they contagious?

Ok I've looked here and on the net but no one seems to know what the incubation stage is on Shingles. Someone I know was diagnosed today with Shingles and the doctor didn't say how long she was contagious....I worry about my mother in law because she was with this person last week and the MIL is not in a healthy state as it is. Thank you in advance!