Im Very Worried And Need Help?

Ok my cousin and me are very close and on june 5th she got in trouble because her parents found out that shed given her boyfriends a ******** and a hand job And he fingered her ok now i know about it and so did our friends Justie and Brooke well when asked who knew she told because shes a very bad lier and then they said we werent aloud over for the whole summer and she was grounded i was mad but in a way relived because shes 13 and were cousins and best friends and i was worryed about her and that she might have well her punishment didnt last long only 6 days and were all aloud back and her Boyfriend is tew so anyways HERES THE REALL QUESTION today she said she was going tew have with him on october 9th and im Confused on what i dhould dew i mean i want her tew trust me but i wanna tell cause she dose stupid things and who knows if shell use a condome with him and shes 13 Im 15 and havent had full on Theres been ual activity but ive never went all the way and shes way tew young anyway please help and theyve planned this even though they dated for only 3 months so far what should i dew?