How to handle family events with a member I dislike (my sister in law)...help!

So long story short, i have my sister in law blocked from my phone so she cannot contact me anymore. It’s been years of me trying to help her through her drug addictions, alcoholism, loosing jobs, and her wedding being called off. She just is a person who cries and wants everyone to feel bad for her, lives off her parents (she’s 34), and wants sympathy. She never takes my help or advice and has an excuse for everything so I chose to block her and not allow her in our home. My husband still once in a while talks to her, but agrees she cannot come over and has taken a step back from her. Anyways, it’s my father in laws birthday dinner tonight and I told my husband I’d say hi and be civil, but will not be any friendlier than that. How should I handle it if she gets defensive or rude, or should I fake be nice? I hate awkward situations, but shesmy sister in law so it’s going to happen. How should I handle this?! I’m so anxious.