According to Canon #943, the minister of exposition of the Blessed Sacrament and the eucharistic blessing is a priest or deacon.
In special circumstances an acolyte, extraordinary minister of Communion or another person deputed by the local ordinary in accordance with the regulations of the diocesan bishop may expose the Blessed Sacrament for adoration. At the end of the period of veneration, that person may return the Sacrament to the tabernacle.
Only the priest or deacon, however, may bless those present with the Blessed Sacrament.
A religious sister could be one of those deputed to expose the Blessed Sacrament.