May I Consecrate My Dying Sister to the Blessed Mother?

First, we are sorry to hear of you sister’s illness and will pray for her.

Second, consecration requires a personal choice by the one being consecrated. So you can’t make a consecration on behalf of someone. However, that doesn’t preclude your asking the Blessed Mother to intercede for your sister, including through your praying Rosaries for you sister.

In addition, you can have Masses offered for your sister and have others pray for her as well. And we’d suggest that you have a priest visit pray with her. She can’t receive the Sacrament of the Anointing of the Sick, but a priest can pray with and for her and anoint her with holy oil.