Maybe he didn't give her time which is valid with her attitude hope she got her toes smack in the edge of the wall....
I think Gramps once said, because she (Grandma) has been there from day one, she became greedy and actually think that she has a stake/owning at least half of Sunyang. Based on that, I assumed, they started to drift apart after Sunyang get bigger and bigger and yet she didn’t get to be President of most subsidiaries.
I can't remember but I think I saw a spoiler about why she's that mad. It felt like she wants to be the "Empress Dowager". She hates Dojun mother that's for sure and she extended her hate to Dojun especially on how the grandpa dotes on him. Threatening her position as "Empress Dowager" she's dreaming of.
But I'm not sure. （￣へ￣）
I wonder what the Grandfather do to be hated so passionately lol