Jealousy

Hi Nicholeen, the problem we are facing more now is Olivia being so jealous of Fiona.
When is Olivia by herself, at home or on the street or church , she is very good, she listens and behaves well, but if Fiona is there is another story, she has tantrums, does not listen, she hits her.
We have try the calm place, the chores the lose of privileges and is not working, she feels remorse and apologize and says she wont do it again, but then is the same thing again, what will you recommend we can do to help her? When we ask her why does she hits her, her response is “ i don know”
Please help. Thanks
Irma