birth control fell out after sex?

[Shady]

ok my sister is 18 and she had sex with her bf the other night and later that same night her birth control fell out and she was freakin out because she said sprems stays in the body for 4 days.so the next morning i said how u feeling and she said i dont fuckin know 1 min on a period than a few hours shes off it and she told me it was very light and she said she has a 50/50 percent of being pregnant so please tell me she isnt pregnant she already got a kid two is gonna be trouble