My girl does not prefer a large dildo. I got her a buttplug, a roughly 5" dildo which she uses most, a roughly 7" cock shaped vibrator (this one is fairly similiar to me) and a Hitachi Magic Wand for the clit. On special occasions she'll use several at a time. She really has to work up to get the 7 pumping nicely.
At least not in my case..just in a few ocasions i can go all the way in with my wife cause she feel pain after 7 inches inside. Only when she is too horny and with extra lubrication I'm able to go completely in. I love that!.