wrt custody of minor child with mother

Firstly, the Petition filed by your daughter cannot be under 13B as you have mentioned it is at the case of cross-examination. It must be a contested Petition.  Your query is not clear but assuming that you are concerned whether custody would be awarded to your daughter or her husband, since the child has been staying with her since birth, the Court generally would not take away the custody from your daughter, unless and until her husband is able to prove that she is an unfit and characterless mother