Even among fans of Sally Donovan (at least as far as I’ve seen), there seems to be general acceptance of the idea that Sherlock’s writers aren’t interested in her as anything more than a mild antagonist for Sherlock.
And on the one hand, it’s really easy to see why people would believe that.
But… I don’t think it’s true. I think the writers have very definite plans for her.
Not that that necessarily means those plans will turn out to be great ones, because who knows. But I can be hopeful for the time being, can’t I?