Will one who dies at a young age (16 years old) be judged like an adult? And will Allah forgive her sins if she was ill before her death? And does seeing her in a dream in a good state reflect her condition?

Allah Almighty is a just judge; He rewards a good deed with ten times its like or more, and He only punishes a bad deed with its like or pardons it. Therefore, there is no need to ask about dying young or old. Illness before death is a sign that good is intended for the deceased, as whatever afflictions befall a Muslim expiate his sins or raise his rank. Seeing the deceased in a good state in a dream is a good omen and indicates the deceased's favorable condition.