Teddybear45 have you read the thread? A mental age of 6-9 is the old fashioned, outdated and misleading way of saying moderate learning disabilities. It doesn't remotely mean that the woman is a 6,7,8 or 9 year old in an adult body.
Adults with moderate learning disabilities can consent to sex in some circumstances. The only appropriate circumstances would be enthusiastic consent with a peer (so someone else with moderate learning disabilities) ideally after talking through her choices extensively with a trusted carer and learning about the consequences of sex and contraception in an age appropriate way.
A woman in her 20s with moderate learning disabilities can have sex without it being rape. Women in their 20s with learning disabilities are not children.
However obviously women with learning disabilities are incredibly vulnerable and she may have been raped.
It is not pure and simple though, nothing about this case is, and treating adults with learning disabilities as children is totally inappropriate.