HELP ASAP FREAKING OUT

So I posted last night about my friend. She lost her virginity last Friday at 2am and took a plan b Sunday at 9. She called me a week later and said she had been bleeding on Saturday with bad cramps. It's now Sunday and she sent me this and says it won't stop. She's 16 so her options are a bit limited. But please help her period should be coming the 22nd but idk why this is happening. I've taken plan bs before but it hasn't affected me a whole week later. I only felt drowsy that day so someone please help because we don't know what to do. We want to take a test but think it's too early. Can someone explain the bleeding? Or just give me some advice.

Also please don't scold me about her age, I see it happen a lot on here but shit happens and I just would appreciate some advice.