oh i know how worried u must be my friend had a son who didnt talk much till late too...
Maybe try and make games out of it or call her mum or dad when u wanna talk to her..
when i call my son i always have a habit of calling them dad lol no idea why...
i used to also put my chin under theres and say mum mum mum and there mouth would open and shut with mine and the noise that comes out would start the sound off and they eventually started saying mum mum mum and wouldnt shut up lol...
if your really worried mayby take her to a pead. and see if there is a reason she is holding back on her speech??
sometimes kids like to do things at their own pace even if it has us pulling our hair out.. GL babe