Four months in, and there's still been no intimacy.

I'm a 25-year-old male, and my girlfriend, who is 20, and I have been together for four months in a committed relationship. Despite our connection, we have not yet had sex, and I find myself growing increasingly frustrated. I’m trying to be understanding, as she is a virgin and I have had multiple partners in the past. In my experience, even when I was 15, I was intimate with a girlfriend who was also a virgin, and it only took us about a week and a half of dating to take that step. Normally, I wouldn’t wait this long, but I genuinely like this girl and see a future with her, which is why I haven’t ended things. I’ve discussed my feelings with her, and she understands my frustrations. She has mentioned wanting to be more open-minded, yet there hasn’t been much change. I feel torn; I don’t want her to feel pressured, but I’m also frustrated by the continual rejection. We’ve had some sleepovers, but aside from light kissing, nothing advances further. She has expressed that she wants her first time to be with me but isn’t ready and isn’t sure when she will be. I plan to have a heart-to-heart with her about this tonight, as it hasn’t been addressed in a while. What are some suggestions for what I should say or ask during this conversation?