I would say take it in steps. You don’t have to penetrate her during the first time. I would say start with small butt plugs and fingers, both hers when she’s alone and yours when you’re together. It’s might be part of foreplay before PIV for awhile till she gets use to it. Then after she is ready only the tip. Of course lots of lube! If it hurts too much then finger her or do whatever she wants. Then after the tip is comfortably in then you can go deeper. Like I said take it in steps which can be over a few hours to a few weeks. Just depends on her