My girlfriend she is bleeding a lot after sex, and...

treatment of vaginal bleeding after sex :
the treatement depends on the cause so you should do clinical examination , and we advice to take rest and avoid sex during treatment and if there is an vaginal infection you can take Metronidazole 500mg 2 times daily for 10 days and if there is blleding tendance you can use Daflon 500mg as recomended by the gynecologist , and if there is an hormonal problem or vaginal dryness you can use estrogen 
Diagnosis :
by take full medical history and doing clinical examination and CBC to detect infection , and examin the vagina and cervix by spiculum and doing hormonal assay (estrogen , progesterone) and pelvic ultrasound 
Causes :

• vaginal infection 
• cervical dilatation 
• homonal problems 
• some tumers 
• vaginal dryness 

Advice :
you shuld go to the gynecologist to get proper managment