sibling drama

D • Mama of 2,lost an angel, waiting on number 4💘💓💘 married-blessed💓
So I'm currently visiting my family in Germany (hubby, the kids and I are living in LA my parents moved to Germany a few years ago) and we're staying at my parents place. My brother is 19 and my sister just turned 18. I LOVE my siblings to death but I just happen to get along better with my brother especially the last few years.
You could say that's because she's young but when I was her age I graduated from highschool and I was one of the best in my whole school and I was pregant.
She's been acting super weird the last few days she like didn't help me with the kids or with the household at all (siblings live with my parents) and whenever I ask her something she just yells at me in front of my children. 
I didnt say anything yet because I just thought maybe she'll tell me whats wrong later even tho it's been like this since like 2 weeks already but she didnt. Instead she brought this guy home no one knows and she literally just said they're getting married.
The problem is I cant really say anything because I was so young when I got pregnant but honestly I want her to finish SCHOOL first and chill out. She said she met him 3 weeks ago and I'm just worried but I dont know what to say.
My husband and I grew up together he lived right next to us and like my parents know him since he was a baby so that wasnt a big deal but my mom just told me to talk to her as her big sister but I dont think she'll listen to me either
What should I do?