Are you the sort of person who can develop attraction over time? If there's a chance you are, it can't hurt to keep dating her and see where it goes. If you're certain you will never find her attractive, it would be kinder to both of you to not waste time, possibly hurting her down the road when you find someone you are attracted to and would rather be with them.

If you do choose to stay with her, don't lead her on at all by giving her reason to think you're really into her when you're not. It may be difficult, but it may come to a point where you need to be honest with her that you're just not feeling it.