sometimes it also depends if you used lubrication some of them my cause them to burn and in some cases irritate when sperm is involved and cause pain. I highly recommend her to go to the gyn so that she could get advised, another thing that you might want to avoid is releasing sperm in her vagina unless you are trying to get her pregnant the reason why is because it can cause infections in the vagina that might lead to other things
Also, there is a "Sexual Health" forum for these type's of questions, best wishes...Judy
She probably has a yeast infection and needs to go to her gyne for anti biotics, I recommend that you abstain from sexual intercourse until she has been treated, but only a gyne or physician can diagnose and recommend proper medication for this. Judy
If it is a burning sensation, could be allergic reaction.