Whats the best way to handle an extremely jealous sibling?

Make the conversations more about her. Ask her what she's doing and how she's doing. Ask her about her job or anything about her. I know it's nice to share your success with other people, but your sister is not the person to do it with at this moment in her life. You can share your success with other family members or friends if you like to of course. What you might not see going on is your family might be unintentionally rubbing your success in her face and you reminding her isn't helping her jealousy much. Try neutral topics instead. Maybe interests you both have or you're interested in something she does.