Dwight-
As others have mentioned here, what your girlfriend does is quite normal, and it may that this is just the way it is.
I am sure you know that there are at least two kinds of orgasms. You and her could look into information regarding vaginal orgasms as compared to clitoral orgasms.
There are more ways to achieve vaginal orgasms than we have talked about here. It also seems to me that vaginal orgasms come with more experience for women, and are easier to obtain as you get bigger.
If it seems it is “one or the other”, you might try talking about it with her. If she isn’t allowing you to penetrate right after, that would be something to try. Lots of lube, and very slow stokes, like one every 5-15 seconds to start. Avoid contact with the clitoris if she is built so that it touches you while coupled. I think this may work well as she seems to be very relaxed, and being relaxed is very important.
It could also work out that she is very surprised at her reaction and feelings if/when she orgasms again or in a different way. I mean she may VERY surprised.
If you two are working at it too hard, the next level probably won’t happen. Just “getting drunk and screwing”, having fun celebrating sex is the first thing to do.
Women in particular seem to have preconceived ideas as to how sex should be. It can be challenging to get them to let go and experience all that it can be for them.
I could recommend many, many things, but one specific thing you may want to try is massaging the muscles in her butt. Deeply massage the muscles, working up in force until you are really rubbing them hard. This will take some time, and it may take several sessions.