The Subjunctive mood is used for improbable situations or wishes. It was very used in British English in the past. In the first part of the sentence, there is a wish expressed by the speaker. He/she wants to god bless his/her mother.
The indicative mood, on the other hand, is the most used. This type of mood is used to make statements or asks questions. In this case, the second part of the sentence is making a statement. That the sister wants the same that the speaker told in the first part.
