It's quite common for Women with ADHD to have trouble paying attention while having sex. Their minds often wander while having sex. For some women that's not a bad thing. I guess it all depends on what the mind wanders to. For many women their mind starts wandering to things like housework, bills that haven't been paid, and countless other things which ruin the mood.
Recently there has been some discussion about this in some the online ADHD Communities. The forum post called Sex & ADD: Can't focus, can't get in the mood has become quite active over at Women with ADHD. Ned Hallowell also offered some advice in his post Distracted During Sex? over at ADHD Marriage.
So the good news is that there is hope and women are able to connect with others who are also dealing with this same issue.