Thin fallopian tube and narrow vagina may be a coincidental finding kindly observe the type of pain , if it starts before the periods and stays for about 48 hours and do not affect ur day to day activity then it is something called dysmenorrhoea a common finding and nothing much to worry about , u can also take some antispasmodics SOS after food

you can start her on tab. meftal thrice a day during her periods. that would decrease the pain by 70%

Thin Fallopian tube and narrow vaginal opening do not cause period pains. If the uterus is normal on ultrasonography, with no collection of blood in it, then the period pain is very likely to be a symptom, which many ladies experience, to different extents. She can try Mefenamic acid tablets for the pain and Tranexamic acid tablets for the bleeding. Both should be taken only during the first four days of her periods. There are tablets which have a combination of the two, as well. Please see a doctor for a prescription.