Isn't it pretty much confirmed at this point that the doujins are canon? It was stated this chapter that she had multiple partners, including adults, which is basically what the doujin are all about. Even that she is bringing multiple guys to her dinner with her dad (her sexual partners).
Back when the manga started, it was hard to tell since it all seemed rather tame, but ever since they had sex, the author seems to be just throwing caution to the wind and making multiple mentions of stuff that fit the doujins. Either that or the doujins are set in the future, but I'm guessing a not too distant one...