To what extent is secret misyaar marriage legitimate, and what is the Maliki school of thought's position on it, for a woman who fears losing her daughter?

Secret marriage according to the Malikis is one in which the husband instructs that it be kept secret from one of his wives or a specific group. Its ruling is annulment before and after consummation if it does not become public (i.e., its news does not become widespread). However, if the instruction for secrecy comes only from the wife, or only from the guardian, or from both of them and the witnesses without the husband, or if the spouses and the guardian agree to secrecy without instructing the witnesses, or if the instruction occurs after the contract, then the marriage is not invalidated.

As for the majority of scholars, they consider a secret marriage valid if its pillars are fulfilled: the woman's guardian, two just witnesses, and the contract formula, and this is the preferred view.