Is there a risk of re-infection after one episode of shingles during pregnancy?

My wife is 22 weeks pregnant. She had a mild case of shingles at 17 weeks. Blood tests show that she is not immune to varicella, but has had chicken pox as a child. We know there are chances of complications in the first trimester and close to delivery. She is a school teacher and is due in March. Chicken pox is common at that time of year, especially around 500 children. We are very concerned. She was planning to work until her delivery. Should she stop working now that she has had shingles and has no immunity to varicella?