Difficult relationship

My relationship with my sister has always been tricky. It’s very strong and we both care about each other very much, almost too much. But she has dealt with mental problems all her life. Bad anxiety to a point that daily tasks are hard and sometimes impossible, serious sleep issues, depression, etc. When we were young I didn’t understand her. I was tough on her. I didn’t understand why she wouldn’t just toughen up. I didn’t have much patience and I felt she was making our family life hard. Over the years I’ve learned to understand better and she has opened up to me about this.

When she is in a bad place which is more than half of the time, she’s very difficult to talk to. She gets triggered super easily and gets very defensive. I do still get very impatient with her just wanting our life to be normal and good and I think she can feel it and is more prone to get triggered by me. I don’t know how to deal with my emotions when I’m with her. When she’s being negative, triggered, and defensive, I don’t know if I should say something, set some boundaries, or just try to be supportive (which seems to be the hardest thing for me). I have a very difficult time saying supportive words and showing that I care about my family. I always have. I love them more than words can describe, but there is something that is stopping me from expressing it.