What's the right balance in supporting your partner to become better (and not make her overwhelming)?

I just told my partner not to do something, and then she said I was being too demanding with my expectations. After reflecting on it, I feel like maybe I've been too eager to 'change' her for the better. I realize that my attitude of wanting to 'change' her might also be toxic, but my reasoning is that I do it because I care and love her. I want to know what boundaries I should set so I can still support my partner in becoming better without overwhelming her or making her feel like they're not accepted as she are. What do you guys think?