How to deal with my judgmental sister and my boyfriend.

I am dating someone who I have been on and off again for a few years. I never shared this info with my sister b/c she is judgmental and we live a few hundred miles apart so the easier way was to avoid it. He served time for white collar crime but has turned his life around and I am very happy with him now.
I've been widowed for 7 years and dated others but I do love the current bf and respect him for getting his life back on track. My sister is VERY JUDGMENTAL and I know she will freak out that I'm seeing him!

The real issue is coming up...I invited her and her husband to the beach where I'm renting a house for a week in September. My kids know I'm seeing him and understand. I invited her before I reconciled with him and I invited him to come with us. How do I tell her and do I make up some story to avoid her coming? Do I just tell her now and also if she can't understand and be cordial, then don't come? I'm so torn, help!