Why was the immigration application rejected after all its affairs had been facilitated and after seeking God's guidance (istikharah) several times, despite drawing closer to God and supplicating that this emigration be His will, and what is the interpretation of this in light of her complete trust in the Istikharah prayer?

Allah is more merciful to humans and knows what is best for them. Emigration might entail religious or worldly calamities, and therefore, Allah prohibited it out of mercy. A Muslim must be content with Allah’s decree. If one trusts in the Istikhara prayer, then it is more befitting for him to be content, submit, and be certain that what Allah has chosen is the best.