Question

Dear Rabbi, hello,
 
There is a secular girl I know with whom I want to build a relationship. As is generally the way among secular people, I assume she will want to have relations before marriage.
 
I accept the law of a concubine, but I think it will be hard for me to ask her to immerse in a mikveh at an early stage of the relationship without turning her off from the idea of being in a relationship with me.
 
So the question is: does a shower count as a mikveh on the Torah level, so that it would then be permitted to violate niddah only on the rabbinic level when the goal is to create a relationship for the sake of being fruitful and multiplying, which is a Torah-level commandment? (And one could also relate to the idea of marriage, which is a commandment according to certain halakhic decisors.) And we are speaking only about a temporary situation, one that I would not agree to continue after intimacy is created. (In that case it would come out that I am causing her not to lead some other partner she may have into the sin of niddah, and overall I would be reducing transgressions, in the style of “desecrate one Sabbath for him so that he will keep many Sabbaths.”)
 
(I do not see this as a “lie” that I am not saying that later on I will ask her to immerse. That is the way of courtship—that not everything is said at the beginning.)
 
Thank you very much.