Good luck with that. Best to take it slow. If she sticks with it, it will probably take a couple of weeks to get all the way in.
That's good advice. It took my wife and I almost two weeks of daily play to get me all the way in her butt. Don't try and get it all the way in on the first try. But, if you're anything like us, you won't need to get it all the way in. I think I just got my head in on the first try, and we both had incredible orgasms. Good luck with your new adventure. I hope you and your girlfriend learn to love it as much as my wife and I do.