I was raised as a jw and can only tell you this: Trying to make them question their religion, is like the dream of every family member of a jw. As far as I know nothing special about Russell. (My grandmother told me once that he smoked cigarettes, and that rule only came about years later)
Was your girlfriend raised in the 'truth'? If so, it is very doubtful that you will change her mind. Although the fact that you "behaved" like that, tells me she will put that belief aside to answer the call of nature.
You could always remind her that the origins of marriage and wedding rings,(though I am married) date back before christianity... some used it as a symbol of "ownership" of the female. Remind her that modern Christianity has borrowed several customs from pagan tradition. Even Jw's. The bread and wine, at passover... a pagan tradition "re-vamped" by the church. (Bread= Earth .... Wine= water... then air... then fire... the elements of Magik. but that is a whole other topic)
But it sounds to me like she has you questioning your own beliefs, if you are even considering it. I would dare to say that most Witnesses raised by Witnesses... dont really know what they believe... they know doctrine... it is pounded in the head since birth. But your girl WILL know that she can lose everything, if she doesnt comply. The fact that she was re-instated, says to me, that she went before the elders and ... repented? for sleeping with you(or whatever you did). If you really do LOVE her, then all you can do is show her that you will love her, no matter what she believes. Maybe, you could introduce her to other options, without making "religion" an issue. Let her know that you believe in "god" and just try to show her that this religion teaches, that man was a mistake, that needs to be wiped out... like God had to start over again, cause he messed up, a SECOND time... according to the bible he already wiped man out with the flood. Sort of a contradiction if you ask me.
If all else fails.... ask her where does the story of creation, leave the dinosaur and the other 60 million years of earths history. (worth a try)
But dont be confrontational. Dont "slam" her religion, or her family....get more flies with honey..... If you slam it, then you only give her family and congregation, more ammunition. Of course all this will pivot on your own lifestyle.... How close is your lifestyle, to that of a christian? I mean, if you are a total "sinner" then forget it.... but if you live a "wholesome" life, you give them less ammo. Cause her peers will say "see how he lives.." anyway, good luck. Love is a fickle thing, and we do much in it's name.