Rent arrears

My partner and me live in a 2 bed flat and my friend was homeless so we told her we would put her up. I was working agency work and in the last month I got no shifts and my partner was off on the sick and only getting £80 which just about covered bills so my friend said not to worry she's got the full rent money and will pay it this month so of course I said thank you and I'd repay once I can! Our rent was due on the 9th and yesterday we got a letter to say our rent was in arrears and hadn't been paid. She keeps saying "I'll pay it tomorrow, my uncle is transferring it" but it never is so now we could be facing losing the house. What am I to do? And yes I know it's not her place to pay it all but she offered