Are they hurting her...Please help!?

Omg im shaking as i type this. I literally have my baby sister in my lap RIGHT NOT and her back is BLACK AND BLUE she JUST got back from dyacare 4 hours ago but she hasnt been put in her jammies and shes not a sleeper so she stays up pretty late. I Went to change her and she started twitching as i went to pull up her shirt I Turned her around her back is black and blue. Im by myself right now as my mom stepped out to the market and my dad is at work and my brother is at a friends house. I think its the daycare! My mom never talked to me about a call from the daycare saying that she had been in a accident, i know this because she tells me EVERYTHING. And knowing my mom she would have been cussing someone out.. please helpppp! what should i doooo