How sound is consulting God for guidance (Istikhara), and why did harm occur despite her praying for two weeks? What does that mean?

One must be content with Allah’s decree, patient with His judgment, and submit to His command. Calamities are by Allah’s permission, and the believer gives thanks in prosperity and is patient in adversity. Patience is an indestructible fortress, and affliction may be for the expiation of sins or the elevation of ranks. Allah is more merciful to His servant than a mother to her child, and good lies in what Allah destines and decrees. It is not permissible to wish for death due to an affliction that has befallen one; rather, one should supplicate with Istikhara, asking for life if it is better, and for death if it is better. One must take measures for treatment, strive in supplication, and seek a trustworthy doctor.