the vaginal wall between vagina and rectum is relatively thin

the wall between vagina and rectum is thin enough that if a girl is fucked in her butt and girl insert finger in her vagina, 

then she can feel his cock with her finger, 

this probably means that sexual pleasure could be felt both in vagina and in rectum, 

which could mean that girls that don't get orgasm from vaginal sex, could possibly get orgasm from anal sex, 

if done properly 

with enough passion, pleasure, attraction, romance and practice