If you had the marriage contract made, the young lady, may Allah have mercy on her, was your wife, although your marriage was not consummated. In other societies, the marriage contract is made on the wedding night and it constitutes the change of relationship. Prior to it, the man and the woman have no formal relationship. If your relationship with the late young woman was of the first type, i.e. you have your marriage contract made, then the whole question should not arise. Whatever you do on her behalf is simply done by a husband for his late wife.
Nothing can be more appropriate.
Some people may question your attitude in doing things in memory of her when she is not really related to you. That is a narrow view. You have made a formal agreement with her and her family that you would be married soon. The engagement is a real relationship although it was not formalized by a marriage contract. That was the next stage which you would have reached had she remained alive.