Although Lyman Ward is ostensibly writing a book about both of his grandparents, he's mostly focusing on his grandmother, Susan Ward. Susan is an extremely accomplished woman, but Lyman unearths some startling revelations that change his perception of dear old granny forever.
From Lyman's perspective, Susan is pretty much the greatest woman who ever lived. She's a hard worker. She's an avid intellectual. And, she's an amazing artist and novelist. We'd swipe right without a moment's hesitation. Actually, we think that this quote about Susan sums up her charms pretty well: "[S]he was the only girl [...] who could conduct a serious discussion of the latest North American Review while scrubbing her mother's floor" (1.1.45).
To be fair, this adoration is firmly backed by the historical record. Susan was indeed "the best-known woman illustrator of her time" (1.1.36), which is actually a pretty revolutionary accomplishment for the era. This fame (along with her natural charm) helps her rub elbows with some serious bigwigs in her time, which backs up Lyman's claim that she was a Big Deal. Finally, the sheer fact that Lyman is staying in a place as swanky as the Zodiac Cottage shows that the Ward family eventually became successful, no matter how stressful their early years out west were.
If you dig a little deeper, however, you'll realize that Susan has her fair share of flaws, too. For example, she's never able to get over the fact that Oliver comes from a lower class than she does. She can't help but compare Oliver to "the figure of Thomas Hudson, in shining mail," who's the sort of literary intellectual to whom she's typically attracted (5.1.4). This causes a great deal of tension in her marriage, especially because Oliver sort of agrees with her.
Still, Susan's greatest flaw is far bigger than a minor quibble with her husband.
Naturally, that honor goes to her shocking affair with Oliver's best bro, Frank. How could Susan betray her family like this? Well, we think that Susan falls so hard for Frank because he reminds her of a young Oliver, before his businesses started failing and their marriage got tense. Plus, Frank is also far more capable of blending into the world of high society that Susan craves so much.
Susan, of course, pays the ultimate price for this affair when her daughter Agnes drowns during one of their trysts. That places the final nail in the coffin of Susan's relationship with Oliver.
So, how are we supposed to reconcile these wildly different views of Susan Ward? Well, we'd start off by simply saying that she's human—there isn't one of us out there who isn't up to their gills in contradictions and dirty little secrets. That's how Lyman interprets it, at least, because he's now able to feel some empathy for the woman who betrayed him, his ex-wife, Ellen. Although Oliver was never able to forgive Susan for her betrayal, Lyman hopes that he will be "man enough to be a bigger man than [his] grandfather" (9.1.240).
But, we're not sure it's entirely accurate to say that Oliver never forgives Susan. Although the couple never actually talks about their issues, they seem to have found a way to live in peace in their last days. After all, Lyman notes that Oliver "had not been dead two months when she lay down and died too, and that may indicate that at that absolute vanishing point they did intersect" (9.1.237).
If nothing else, this shows that when everything is said and done—when Susan has finally settled into her "angle of repose"—she realizes that she has had someone propping her up, after all. After everything she's been through, this must be a truly comforting thought.