I think the only thing Taina can do for redemption is to get the mc his sister. That was her promise from the beginning so far you helped her get what she wanted and she has not lifted a finger to help you only herself.
I don't think that would even "redeem" her.
I'd say the majority of the issues you had to deal with were either directly or indirectly caused by Taina. If she had cooperated in earnest with the mc from the get go, we probably would've had the sis.
I'm guessing she was the information leak leading to Fu's blackmail, probably convinced the queen to prevent the marriage, probably used Taina to cause chaos in her own home to get the queen to undermine the mc's efforts to get the sis.
An analogy: Offering someone a gift, then stabbing him in the gut, then saying "the original plan was stabbing you in the heart" then providing them with a trip to the emergency room and offering them the originally promised reward isn't a redemption; it's just the person turning out to be less shitty than absolute sewage tier.