sisters betrayal

My family owns a business for 32 years , its me my brother and father. My sister was never part of the business, until her husband passed away. Then we hired her to do all the bookkeeping. years later we find out she had been steeling from the business, with the results of us almost loosing everything. We confronted her with the evidence and have not talked to her in over 3 years. She has two daughters, who we have a relationship with. One of them is getting married in June. I told them I can’t go unless my sister owns up to what she did, and that i would talk to her from a place of forgiveness. I can’t go and act like nothing happened. My model is
C My Sister
T She stole from our business and hurt our whole family
If she asks for forgiveness. I will forgive her
F Betrayal and hurt
A Talk about her, but not too her
R No relationship

C Wedding
T I can’t be in the same room with her and just pretend
F Angry, hurt, sad
A Try to get my niece to tell her how i Feel
R Unsure