What is the ruling on girls using oils and popular remedies to lengthen eyelashes and whiten skin? And does this count as altering Allah's creation?

It is permissible for a woman to use permissible herbs and foods in cosmetic recipes, whether for treatment or beautification, due to the generality of Allah's saying: (He is the One Who created for you all that is on earth). This is not considered the blameworthy alteration of creation, unless the change is permanent and continuous. It is preferable to opt for other materials if possible, to avoid the suspicion of extravagance or disrespecting food.