The fact that your friend had a reaction to lavender which she applied to someone else indicates that the personal care products that have been used over time (soaps, shampoos, dishwashing detergent, deodorants, hair products, skin care, etc) have become deeply imbedded in the tissue.
Pure, premium essential oils work to detoxify the body, so when they are introduced, the toxins are “running for the fastest exit”. That would be the skin – the largest organ of detoxification on the body.
Because there was such a strong response, it would be better not to use the oils until she is a little less toxic. She can improve things by drinking a LOT more water. 2 liters a day is the minimum amount. When there is a toxic response, then it should be increased to at least 3 liters a day.
Rashes indicate acidity. The three most significant things that increase acidity in the body are what I call the “Three Poisons” – SUGAR, CAFFEINE, and DAIRY PRODUCTS (cheese, milk, etc). There are many other acid-forming things that we consume, but focusing upon those three will make a huge difference.
If she stops using the chemical-laden personal care products, she will more rapidly come to balance.