Statutory rape
No it wasn't. There is no such crime in the UK. In this case, since the victim was over 13 and apparently consented, the offence would have been sexual activity with a child.
I tend to think it's lack of evidence and reasonable double the rather than they didn't actually do it
There is a third possibility which is that the jury concluded that the victim did not consent but the accused reasonably believed that she did. I would also add that in a significant number of cases the judge directs the jury to acquit on the basis that the evidence is too weak for a conviction. The evidence has to be VERY weak for that to happen.
but the car she claims these things happened in wasn't even there so struggle to believe her
I took that as meaning she had misremembered. This can happen with historic cases of sex abuse. In this case she appeared to vividly recall details that could not have been true, thereby undermining her evidence. She also had to admit she would be paid a large sum of money if RC was convicted, undermining her evidence even further.
Poor finish. Lots of unanswered questions.
Disagree. Yes there were lots of unanswered questions. My view is that it would have been a much weaker drama if it had attempted to answer all of them.