I am sorry about your sister, how sad it is to watch someone we love self-destruct.
My son has been homeless many times, I suspect he still is today. One time when he left a men's shelter to go to detox and then to a rehab, I had to go to the shelter to pick up his things. The Salvation Army man took me upstairs to the sleeping area and where my son slept to get what was his (and leave what was not). He talked to me while I packed up my son's few belongings and I learned that it was the shelter that hooked him up with a rehab and that there were counselors there to try to help those who needed assistance. I've never been afraid of the street since.
Your sister may find a shelter, or somewhere else to continue her drinking. But this losing her home and having nothing may actually bring her closer to reaching out for help. I pray it does.
Prayer is pretty much all we have, but it's what keeps me sane every day, knowing that God can do for my son what I cannot.
Hugs