facebook

hi guys, i just want to ask something:
on facebook im know my girlfriend password and i can log in when im want..
but she live 1500 miles far from me for a short time.. and im working too mutch and if she cheat me on facebook she can delete it easy... can anyone tell me how can i get all her messages from facebook? i was using family keyboard but thats only for pc or laptops.. and she using phone actually.. thats helpfull if anyone can tell me maybe there is chance for i will get all her messages to one doccuments or something cheers