Anderson (Clinical Pharmacy, Vol 10, Aug 1991, p.612) states:
Breast-feeding is not a contraindication to the use of any vaccine in the
mother.
He references:
Immunization Practice Advisory Committee.  General recommendations on
immunization.  MMWR. 1989; 38:205-27.
I know that the reference is a little old, but the recommendation includes
Smallpox Vaccine, and I don't see why the recommendation wouldn't hold for
Varicella Vaccine also.
This is the best I can do in answering the question about whether Varicella
Vaccine is safe for a breastfeeding mother.
Frank J. Nice