UK council housing.

This post isnt relating to me as I'm only pregnant with my first. My partners sister has just found out she is 8 weeks pregnant with her 3rd child, she's only 21 so she's very worried as she's living in a 2 bedroom council flat currently. She has two boys at the moment and they share one bedroom and her and her partner share the other. When her third child has arrived will the council view her as a priority for new housing as she will have 3 children in a 2 bedroom flat or will they view it as she already has a safe place to live? Anyone shed some light shes going to check with the council but she just wanted to know if anyone has any first hand experience?