I have been making my own bath salt concoction for over 13 years now and some of my most loyal customers are women and children who also suffer from severe eczema. They literally swear by it, and honestly, I have just mixed normal store bought items together you can find anywhere....
Make yourself a big batch with the following ingredients:
2 C Epsom Salts
1 C Sea Salts
1 C any other salt you can find: Kosher, Dead Sea, Table Salt, Himalayan, Hawaiian, etc....have fun.
1 C powdered milk
4 packets of colloidal oatmeal, or 1 cup if you can find bulk
10 T Grapeseed or Extra Virgin Olive Oil (grapeseed is 9x higher in Vitamin E, so that's my first choice)
Pure Essential Oils for aroma. You choose, or have your daughter choose a scent.
Most stores now carry a pre-scented Epsom salt bath soak...You could also try those and just add the oatmeal, milk and essential oils with a splash of oil.
Another fun addition are bath herbs. I would recommend adding a bag of Celestial Seasonings chamomile tea to the bath water.
People tell me all the time I should not give my recipe away...but I would rather you heal and feel better than trying to peddle my bath salts. You can also google bath salt recipes...there are thousands.
Add a good cup of the above to a warm bath, jump in and enjoy. Honestly, she'll sleep like a baby again.
Hope she feels well soon.