How can a friend who fears jinn and imagines them materializing to her, despite her recitation of the Quran, be calmed, and what can she do to feel at peace in her home?

Most likely, what afflicted your friend is a type of illusionary magic (sihr al-takhyeel). The Prophet, peace be upon him, was afflicted by magic before, and Allah sent two angels who informed him of the location of the magic. The cure for this affliction is to seek refuge in Allah Almighty, humble oneself before Him, and frequently engage in the remembrance of Allah and the recitation of the Quran with contemplation and humility, for in it is a healing for what is in the breasts and a relief from worries. It has been reported in a hadith that whoever is afflicted by worry or sorrow and supplicates with a specific supplication, Allah will remove his worry and sorrow. If the symptoms persist, she can present herself to someone whose religiosity and piety are trustworthy, and who is known for ruqyah al-shar'iyyah (Islamic exorcism), while being extremely cautious of charlatans and impostors. What she is experiencing could also be envy or whisperings (waswas), and not necessarily magic.