Could be she is shy and overwhelmed by her surroundings. Give her time, she will come around in the socialized atmosphere of children her own age.

Tick

How do you know this? Who told you this this?
You are not at school so explain who told you this.

Give her a time,

If she has been at home with you until this point then she might just be overwhelmed at the major change in her life. If she's been in the same daycare, then there may have been an incident that triggered the speech loss.

I realize this was posted a while ago, but since you haven't given an update I thought I would still comment. I hope that your little one is doing better.