I guess she has a bank account in single holder mode? Do regular transactions like deposit and spends via debit card on it. May get preapproved offer for CC. (May take 3 months+ minimum)
Quick way to get started: check if she gets onecard (maybe FD based but will build cibil gradually). Have you checked her cibil yet? Also for secured fd based cards, get a higher amount fd not less than 10k.
Add-on cards affect history of primary holder only.