Use sarna lotion on her. today its stinging and continues to make her itchy. it's not red or swollen i stop using it. could her skin be resistant?

Sarna use: Sarna contains menthol (0.5%) and camphor (0.5%) which some people may not tolerate or could sting if there is any open skin. It is designed to help a "general itch" from dry skin, insect bites, sunburn or contact with poison ivy/oak/sumac. First try using a thick moisturizing cream (CeraVe) or emollient (Aquaphor), and you may need to see a dermatologist for a prescription if it doesn't improve.