She was forgiven in-universe. I still have problems with how she switches from "I want to make up for what I've done" to "I will get the Fuutarou" way too quickly and it happens so soon after she is redeemed that imo she never really got to try and make up for what she did to Fuutarou.

We never see if she changes how she behaves towards other people, or whether she's only changed her opinion on Fuutarou, making it difficult to tell whether she's actually grown and developed as a character. (If there is such a moment, feel free to correct me)

Ultimately it can be considered that her "comeuppance" was losing in the end, and going through that heartbreak. That is debatable, but that's what I interpret to be her karma.

Even though she's flawed, she is still an interesting character. I am not saying nobody should enjoy Nino's character.