What can be done religiously, ethically, and morally regarding a daughter married to a Christian after a long estrangement from her?

A Muslim woman is not permitted to marry a disbeliever, by scholarly consensus, based on the Almighty’s saying: "And do not marry polytheistic men until they believe," and His saying: "These [believing women] are not lawful [as wives] for them [disbelieving men], nor are they [disbelieving men] lawful [as husbands] for them [believing women]," and His saying: "And never will Allah grant the disbelievers a way [to triumph] over the believers."

The Muslim woman should be advised to abandon this forbidden relationship and separate from this person, and he should be invited to Islam.

Muslims are also advised to avoid residing in Western countries unless there is an urgent necessity, while emphasizing the importance of teaching children Islam and protecting them from forbidden relationships.

As for the phrase "fate willed it," it is impermissible, for fate is an abstract concept and has no will. Will belongs to Allah alone.