little sister left home...

Okay so my sister just called me in tears because she had a big fight with our mom and she left the house (she’s 15).

She insists that the situation is irreversible and does not want to work it out. She is asking if she can stay with me. I’m 25, two kids and one on the way. I do not have the place, or the resources to take care of a 15 year old. I know my sister is just being stubborn and eventually everything will work out but how do I tell her no? I feel kind of bad about it but at the same time... she’s the one refusing to work things out with my mom. Help!