My mum might leave me?

I live with my mum and my sister (9) and my dad lives abut 45 mins away with his partner. This morning my mum lost it over toothpaste (i know weird? i don't know why) and screamed at my sister and me saying she might walk out and leave the two of us to cope on our own. I'm 15 and really don't know if she was bluffing or not. What should i do without talking to my dad?