If they follow the book, she's not a weak character. Maybe a bit towards the end, like say the last fifth of the book? But by then, her main 2 enemies aren't her enemies anymore either. She's different from Karakade but still has an attitude. Reynu is an underdog while Karakade is the Queen Bi*** lol. She's sincerely nice to people who are nice to her and she'll fight back with people who are mean to her. She doesn't get physical like Karakade, but fight back with words and scheming. And her plotting and planning don't really involve hurting other people directly, it's more to get what she wants.
For example, there's a part in the book where her mother-in-law locks her out of the house and their store and so to get sympathy from her husband, she acted like she was forced to sleep outside the store the whole night but really she went to sleep at her friend's place. She went back to the store in the morning when she knew her husband was returning. That's the kind of scheming she does vs Karakade planning to drown someone lol.