The only things I can suggest right now are to haunt Pike County archives, and to check out as many marriage records of Daniel's children as you can. If they are useful they will give the names of their mothers. Knowing their religion may help find a church record. That might be some work. Also it's possible - if they were the kind of family to keep a bible - that one of the descendants has a bible.
Where are the original names you are getting here for the wives? Did you find a death record or burial record for wife number one (that would be pretty early). Sometimes you can't find one record, but can find proof through other means. Perhaps Rachael's death record will give her former name? Perhaps the death record of one of her children will give her name? I don't know what is available for Indiana, as it's not a place I am used to perusing.
Mary Ann would have had to die, and Daniel marry Rachel, all between 1834 and 1851. This is, of course, assuming he did actually marry Rachel. In 1840 the female in the house is 20-30. In 1850 Rachel is 28. This could mean nothing, but it's possible that the woman in the 1840 household is actually Mary Ann. (I wonder if the Elijah LANE next door is Mary Ann's father?) This would narrow down the marriage to 1840-1850. It is possible that Rachel and Daniel did not marry in Pike Cty.