This is so sad :(
keep ringing the authorities, don't give up!
I pray for the mum, children and their dog x
Sadly theres not much you can do, I mean you've called the police and children services in, and neither has stepped in to stop her father.
The 5 year old is desepertley looking for a safe place, something or someone to latch onto to escape the abuse. I know it may not seem like much but you can be her safety net- Give her your number and tell her whenever she gets scared she can call you, she can come over whenever she wants, if she needs a safe bed to sleep in at night allow her to come over. It may not stop the abuse but you'll be making a huge difference in this girls life, you'll be saving her on so many levels.
Good luck.