Regina runs into Kathryn at social functions. Those strangely satisfying victory celebrations at Granny's that she is being invited to regularly these days. Town council meetings and the occasional Charming family function. They smile pleasantly in a vague sort of way. Like two very well trained noble women who know how to behave in polite company even if you despise each other. Except she doesn't despise Kathryn. She never really had an opinion about Princess Abigail in the Enchanted Forest. If she'd met her there she likes to think she might have tried to save her from the incessant marriage-based-alliance building Midas was intent on. She'd been lucky Frederick was an acceptable political match even after Charming's random act of heroism.
And the truth was, like many things she'd like to have imagined she'd have done when she was Queen, she knows she wouldn't have done it. Regina never wanted to be Queen, but that didn't mean she hadn't always had ideas about what good might have been done with it. After all she was her mother's daughter and the idea of power wasn't foreign to her before she married the King. And after she married the King she had decided feelings about gray haired men deciding who their intelligent and quick witted young daughters should marry for their own gain.
Except Snow always got in the way. Or rather her own obsession with Snow got in the way. And that's what had happened in Storybrooke. She'd found herself, really through no doing of her own and no intention, with a friend. Probably only the fourth in her life, counting Daniel, Tinkerbell, and Maleficent. Though really she probably should stop counting Maleficent. But the curse's hold was weakening and Snow and Charming managed to find each other. Because they always found each other like the lost dogs and dinosaurs of the children's movies she used to watch with Henry.
And instead of comforting Kathryn she'd decided to murder her and frame Snow.
Because it seemed like a good idea at the time. And really, at the time and at no point in the previous forty years had she been much of a judge of what was and wasn't a good idea. And never when Snow was involved.
Looking back on it now, with some limited ability to examine her own past actions, she actually had cared about Kathryn. It'd been nice to have a friend. But she did what she always did. She destroyed everything she touched. Not just the friendship but the friend. Sometimes when she saw Kathryn at these parties she imagined trying to talk to her. Really talk. Like Snow does with people. She imagines that she'd try to explain that she didn't know how to be a human being, and that she was so sorry for that horrific few weeks near the end of the first curse.
And then she remembers that Kathryn doesn't owe her anything. And that she had no right to expect even her time. Some friendships couldn't be repaired. Some things couldn't be fixed. So why bother trying?