Sanders/Saunders Family of Maine

I'm wondering if anyone can help me confirm or disprove a family story.

My great-x4-grandfather was Joseph Foster Sanders (1812-1898). My great-grandfather John Sanders Cross (1883-1963) told a story about an aunt Phebe of his. Previously we had thought this was Joseph Sanders' daughter Phebe Ellen Sanders (1844-1932), aka Nellie. But she is almost consistently called Nellie, so now we think maybe he was talking about a different relative named Phebe. In addition, we have a picture of our mystery Phebe who was usually thought to be Nellie, but we realize now that the two don't look alike.

The theory is that our mystery Phebe is a sister or possibly aunt of Joseph Sanders. However, I'm fairly confident that Joseph's parents are James Sanders (b. abt 1774) and Lydia Foster (b. abt 1774) who were married 3/25/1796. Their known children are James (b.1796), Joseph (b.1798, d.1799), William (b.1799), Elizabeth (b.1801), Nancy (b.1804), Susanna (b.1806) and Daniel (b.1808). Nothing else is know about James' and Lydia's parents or siblings, but I don't think Phebe is from the Sanders family.

So now I'm thinking maybe Phebe is a sister or aunt of Joseph's wife, Jane McLellan Patten (1811-1887) who he married on 4/3/1834 in China, ME. Unfortunately, I have not been able to ascertain her parentage. I had suspicions a while back that this was actually her second marriage, with McLellan possibly being her maiden name and Patten her first married name.

If anyone can expand upon or disprove any of this, I would really appreciate it. I've been stuck on my Sanders family for years, but am hoping this mystery Phebe can help shed some new light.