I too would consider adopting another kitty. I sort of disagree with the behaviourist. In the beginning it is like bringing in a total stranger, but weren't our best friends total strangers at one time?
If it were me, and I am speaking only for myself, I would look into a young male (orange). They seem to be able to get along with most anybody/kitty. All of my males have not had a problem letting the females be dominant. You know how girls are!! I'm sure it would take time but all kitty introductions need time for adjustments.
You know Lucy and her personality so you could speak with someone at a shelter that would help you choose the right cat to be Lucy's new friend.
You have to remember that you will never ever be able to replace Gi. That would not be what you are attempting to do. You would simply be trying to help Lucy and have the benefits of rescuing a poor kitty in need. The best medicine to help you begin to heal is laughter and an occupied mind. Introductions would definately keep your mind occupied and if they become friends then I'm sure you would smile.
Don't feel guilty for trying to ease some of the pain in your heart. It doesn't mean that you are letting go of the memories of Gi.
I'm sorry for your pain and I'm sorry for Lucy.
This is just my opinion and what I would do. Life goes on for us here and all we can do is be thankful for the memories of those who left before us and continue to make new memories with others that are still here.
God Bless you and Lucy.