The OP said the person should never be married in the Catholic Church, not that they should never be allowed to marry anyone at all or in any denomination at all.
The short answer is that there is a right to marry, it is a serious right, and barring a canonical impediment already declared by the Church, the Church will defend the right to marry.
Can. 1058 All persons who are not prohibited by law can contract marriage.
**Can. 1073 **A diriment impediment renders a person unqualified to contract marriage validly.
Can. 1075 §1. It is only for the supreme authority of the Church to declare authentically when divine law prohibits or nullifies marriage.
**§2. **Only the supreme authority has the right to establish other impediments for the baptized.
Can. 1076 A custom which introduces a new impediment or is contrary to existing impediments is reprobated.
The Church says:
Can. 1085 §1. A person bound by the bond of a prior marriage, even if it was not consummated, invalidly attempts marriage.
§2. Even if the prior marriage is invalid or dissolved for any reason, it is not on that account permitted to contract another before the nullity or dissolution of the prior marriage is established legitimately and certainly.
If the OP knows that some person has already contracted a marriage that must be presumed to be valid but that this prior marriage is being hidden from the Church, then that would be reason to try to intervene. If she thinks one spouse is deceiving the other spouse in order to obtain consent, that would be a reason to intervene. It must be something like that, though. The Church is not going to deny people their right to marry each other because some third party thinks the marriage is doomed to fail, not unless the third party can point to a canonical impediment.