My 20 month old just starts crying when relatives try and get friendly with her, she doesnt play with other kids too,likes to do her own bit..how can i make her more social?

My 4 year old hated everyone but me an her dad until she was 3. Now she loves everyone a little too much. It takes time preschool helped so much an just in the nic of time with another one on its way 🙂