There is a chance she has an STI which can cause painful sex, bleeding during sex, and abnormal smelling/color discharge. HOWEVER, in my opinion she probably has a UTI or yeast infection. Both causes swelling of the vulva and vagina which would cause pain during sex. UTI often cause woman to frequently have to urinate yet it is painful and not much comes out. Yeast infection often causes burning while urinating but the main symptom is itchiness. Its best she sees a gynecologist or health provider.
Pain during sex can be caused by a few things i had the same pain a few months back firstly i recomend getting tested for sti or even bv and she can ask for the gp to examine the curvicx and vulva i had the pain due to urine infection but if pain only happens at cirtain times in her cycle than take into consideration that womans curvix changes position during her cycle so when the curvix is low and easy to reach intercorse could cause pain it could be normal if its not all the time and only occurs cirtain times of the month hope this helps