Hi Kathy,
If you don't mind I'd like to post publically in the hopes the exposure will bring keys to our families pasts. Unfortunately, at this time, I don't have any information beyond Walter McFarland. However, his Great Grand-Daughter (my grandmother is still alive. She just turned 95. I have her as a 'living resource of information', but I have to catch her when she's feel ing up to it.
I think your theory of Susan being Walter's sister is a valid train of thought. I felt confident the Rackliff's and McFarland's were connected somehow. Also, Walter McFarlan'd's daughter Lewella (my GG Grandmother) married a Davis.
Additionally, I have seen family tree postings from a Scott McFarland on the net. Although he has not traced the lineage past Walter, he has several trees from Walter McFarland's brood. So, he may know of a possible connection with Susan Rackliff/Radcliff.