I thought this was going to go down a severely wrong path for a minute there.
I have a feeling that your grandmas soap was not a product of the lye mixture as much as a product of the fats used for the soap. Do you remember what she used for the fats?
From what I gather. Wood ash produces Calcium Hydroxide or Potash. Commercial "Lye" is Sodium Hydroxide. You can't get commercial lye from wood ash. You get it from Calcium Carbonate and other chemicals.
Calcium Hydroxide produces a softer soap which now days most people use for liquid...