In the Australian interview it is her facial expression that gives the game away. She has a look of near-panic when the dress pops out the way it does and it is obvious that she is thinking "SHIT".
And even if it is a maternity dress, it really has no reason to be edging forward at such a sharp angle. It is quite clear to me that there is something pertruding from underneath the dress like padding of some sort.
she is tall and the chair was very low, i wonder if the expression is that she didnt realise how low it was and also she seemed to be holding onto her dress to make sure that the guy doing the interview didnt have an eyefull of her undies
I'm sure we have all sat on a chair and it was either lower than we expected etc...maybe that was the surprised look on her face. anyway just another thought on it.