It could be a lot of things so she needs to go to a doctor to make sure. It could be anything from a tipped uterus to cervical cancer, but she needs to go to a professional for sure and if I were you I'd be making the appointment ASAP
You need more foreplay. Get her good and excited and she shouldn't feel pain, maybe a little (it just depends on how both of you are built down there) but the more excited she is the better it will be for both of you.