. If she doesn't let her know IT'S OK, and it's nothing wrong with it. (if you keep pushing her to join the group, when she didn't, she may think she did something wrong and feel bad about it. That will make her feel bad about herself, if she feel bad about herself, the she wouldn't want to join other children to play, see the cycle....)
"Good parents give their children Roots and Wings. Roots to know where home is, wings to fly away and exercise what's been taught them." --Jonas Salk.