Question

My girlfriend (my future wife, God willing) is not religious. She’ll respect my requests, but I want to ask as little of her as possible, because all the whole business of purity checks and so on could really bother her a lot (I think she’ll manage the immersion). What is the minimum that must be required? Is a hefsek taharah and an examination on each of the seven days an absolute obligation according to Jewish law? 
And after the fact, what if she did not examine herself, but knows that 7 days have passed since the bleeding stopped?
It may be that my questions don’t cover the whole topic, since I myself am not completely knowledgeable about it and have only picked up bits of information here and there….
 
I’d be glad for your advice. I stress that I am not asking for a “way to minimize prohibitions” (which you do not provide), but for a way to aim for the halakhic minimum. I’m willing to rely a little on after-the-fact rulings, hoping not to violate clear prohibitions.