Making friends

[Cecilia Prinsloo]

How do I go about helping my older cat (not Maine Coon) accepts Max, my Maine Coon? Max is now 5 and a half months and Piatti is about 5 years old. She, Piatti ignores Max completely when he wants to play. When Max tries to play she just gives him a slap and walks away. It is heartbreaking to watch Max trying to play with her. I'm thinking of getting another Maine Coon but my husband doesn't want another cat. We tried giving her more attention but it still looks like she is irritated with Max.
A friend suggested using pheromones to get her to like Max, what do you suggest I do?
I would appreciate your commends.
Piatti and Max when Max was 3 and a half months old
Max, now 5 and a half month old