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?

Your child is most likely an introvert and you shouldn't be forcing social situations on them as it would make them anxious. Try introducing new people slowly. Maybe 1 person at a time would be a good start and give her some time (multiple meetings) to get comfortable with the new person before getting more people to meet her.