Rodmilla never stood a chance to care about Danielle...

Well they were stacked against each other from the start, and doomed to be enemies.

I mean, Rodmilla:
- Came from wealth (and thus has the expected flaws that come with it, even Henry had some of that in him just remember how he humiliated Danielle at the ball)
- Was married to Auguste in a forced marriage most likely (how otherwise would she hardly know him?), out of necessity (think Kate Winslet in Titanic). That hardens one's character no matter how nice Auguste actually was.
- Resented marrying bellow her class (she a baroness, he a commoner), remember her "you can't leave me here!" when Auguste kicked the bucket.
- Resented Danielle before she even met her (thanks to Auguste talking about her nonstop).
- Literally came to hate Danielle due to Auguste giving Danielle his last words instead of her (couldn't he have said "I love you BOTH"?).
- Was already saddled with 2 daughters of her own.
- Was saddled with an estate she had no idea how to run, nor even intended to run.

WTF did you expect?
It's obvious Danielle was well aware of this, and taking that into consideration spared her life and shipping to the Americas.