I don't think she's a prison visitor, rather one of those women who fall for violent prisoners and write to them.
Radio 5 this morning had a piece on the sound quality. A number of sound techies phoned in to say that's the issue, poor tech control, rather than mumbling actors.
It was gratifying to hear lots of northern accents amongst the people who phoned in to confirm that despite being from the area in which its filmed, they were struggling to hear. One sound engineer complained that (like me) he was having to put his volume up and down throughout the show, music too loud, voices often too low. He said it could be sorted out simply, he named the techie thing needed but of course, I can't remember it.
Lona, I suspect you're right and the 'other woman' is the same one that Claire's love interest was involved with when his marriage broke up. I do hope Claire gets back on that wagon