I have extreme dry skin from Sjögren's syndrome. I wouldn't bother to waste my money on all of those expensive oils. My standard recipe is olive oil/lard/coconut oil/castor oil at a rate of 40/40/15/5 (SF at 8%). Since I've started using my home made soap, my skin has improved 1,000%! I won't use commercial soap any more unless I'm out and about, and I do notice a difference when I wash my hands at restaurants and other places. I also love a good 100% lard bar. I need to make a batch of that.
Others may chime in and tell you their opinions, which is perfectly fine, but I think you should make two small (half pound each) test batches for your aunt. One that is 100% lard and the other with the recipe I listed. Let them cure for a full six weeks. Then let her try them out for a few weeks each to see if either of them (or both) have any effect on her skin. Ultimately, only she will be able to determine what will work for her skin.
I also love my 100% coconut oil soap with 25% salt and 20% SF. That makes my skin feel squeaky clean but well moisturized.
Good luck and I hope you find the perfect formula for your aunt's skin.