Steer that broad middle course between always asking how she's doing and never asking.
And it sounds like you're doing really well, giving her a hug when you see she needs one and telling her she's nice, too. And when you make mistakes as a family member, and you will, and it's okay, please try and view the mistakes as texture. And I think there is generally trial and error and tinkering with medication. Perhaps occasionally, without being overbearing, ask her if she feels her doctor's an okay listener.
And try and be open to free positives. For example, maybe helping with rescue animals or feral cats, maybe getting involved with anti-corporate political activism (I mean, think big issues), or a local road running or poetry group. Nothing is more boring and dry than a life filled with obligations and 'working' on problems. Free positives are a very good thing, for both you individually and for your sister. Be there as a real person and be there in a steady eddie fashion, especially when she really needs you, and also take time for yourself. And I know that's a balancing act.