Sorry for your loss.
Chicken social behavior can be surprisingly complex. If you had two best friends and one of them died or moved away, would you accept a random third person as a friend to replace her? Maybe, depending on the person. Maybe not.
Well, in my experience, chickens are just like that. Daisy and Lexie might eventually welcome a new third chicken with open wings, or they might not. I think the best approach is the "look don't touch" method. You can search on this forum for detailed descriptions of how it works. Basically, you let the hens see each other for a period of time without physical contact. Then when they've gotten acquainted this way, you let them mingle under supervision. See how it goes.
We have a flock of ten and nine year old hens who hatched and grew up together. Some individuals are just enemies. I split the flock into two groups, putting the "mean girls" in their own separate pen. Each chicken has her own personality; all we can do is observe and try to manage housing so that the flock is as stable and stress free as possible for most members.
Good luck and let us know how it goes!