As the film progresses Will does start noticing Louisa in others ways ie her breasts, when they laid down on that bed and then fade to grey. did they do with each what they could or was it just a chaste platonic sleep?
Even though Will was a quadriplegic there is still a chance although a slim one he could achieve a boner. Failing that he could with the help of Louisa of course either inject the penis, use a vac pump, or take tablets such as viagra etc. Obviously Louisa would need to mount him, but the reverse cowgirl position would lessen any distraction caused by her eyebrows