Prisoner Cell Block H by Henry Clement

The blurb on the back:

Women behind bars
Franky Doyle is Wentworth Prison's number one hard case - violent and uncontrollable, a cell wrecker and a bully. She's doing life for armed robbery and murder - and she's spending a lot of it in solitary.
Franky cares for nothing and nobody, not even Karen, whose dark, brooding beauty conjures desires in Franky that can never be returned. Nobody that is, except her kid brother Garry whom she brought up single-handed. And if misfortune should befall young Gazza, then Franky will tear Wentworth apart - brick by brick.