Is the marriage contract valid, and is it necessary to renew the contract in case of doubts about its validity, bearing in mind that renewing it might be considered a divorce for the woman?

For the validity of a marriage contract, it is a condition that it be concluded by the woman's guardian (wali) or his agent. If the guardian deputizes someone else to conclude her marriage contract, the contract is valid. Based on this, the marriage contract is valid and does not need to be renewed.