I would look for a new playgroup but go one last time to make the big announcement (i.e. "Just wanted everyone to know that it is my last day because...... and for those who would like to meet up as a mothers group, feel free to come and grab my number).

I would also speak directly to this lady calmly but in the group so you have witnesses and explain to her personally that she is very judgemental and has caused great distress, all because she couldn't use some common courtesy and talk to you. As such, not only are you going to leave and make a complaint but others are also planning on leaving due to her bullying behaviour.

Finally, I would also complain to the church running the playgroup and also Playgroup Australia (I am assuming you are a member).

Leave with your head held high because her head should be hanging in shame.