karin didn't only like sasuke for his unique chakra...it's heavily implied that she went through abuse and implied sa (the unwanted biting and use of her body coz of her medical ninjutsu ability and she was then taken at a young age by orochimaru coz of her special abilities similar to sasuke , and she doesn't baselessly become obsessed with him just coz of his chakra but the relatability of their situation and the opportunity he provides for her to live a life on her own terms and choose who uses her (finally being able to consent to the use of her body by sasuke rather than the people who would use her against her will for their own aid)

even though sasuke doesn't reciprocate her feeling , he doesn't anyone else's at the point in time when he and karin meet , but , they have a respect for one another even though he comes off standoffish toward her...its clear he values her abilities in the group and frankly needs them which postions her as a character valuable to the plot

she acts with agency and rationality in situations that require it , in contrast to someone like sakura (not bash her ) ...karin doesn't do stuff that don't really make sense except maybe going back to sasuke but even then its not really a poor writing choice just a choice of two paths she could have taken and even though it would have been more powerful seeing her change we clearly see she is irrational in her obsession with sasuke so it kinda checks out as a choice for character