Parents are sending invitation to all the guests on the wedding of their son.
Their daughter is already married.
Can her name be mentioned somewhere in the wedding card of her brother's marriage.
If YES then WHERE??

Why? It is not her wedding? Did she act as a parent raising one of the people being married.

I have never seen a sister mentioned in a wedding invitation

Traditionally it is only the parents of the bride and the parents of the groom who are noted on the invitations. Siblings and other family members are not included.