As someone who was very tight I suggest you to warm her up really well beforehand, try inserting one finger first, when she gets used to the feeling put another one, the same she get used to it you put the third finger there. All of the fingering with a good lube. Of course there will be friction and it will be uncomfortable at first but she will get used to it. Try inserting your penis really slow with short thirsts. MORE LUBE, lube is never enough even when you start fucking her you add more and more. I am not joking it really helps reduce the friction. She will experience pain of course but try calming her down by speaking to her. If it gets too much for her stop. Try again a couple of days later. This is a process, don't expect it to happen overnight. She also needs to be fully relaxed down there. She will get used to it eventually, just stay patient and supportive!