My sister is on Social Security Disability and is moving into an Assisted Living. She was told that all her Social Security will go to the facility.

The last time I looked, this was still the United States of America. Let's hope it stays that way. As Igloo said, most states do NOT have a waiver that pays for an Assisted Living Facility automatically out of one's Social Security payments.
One should be able to KEEP their S S checks and pay for A L by writing a check themselves or by enacting an LTC insurance policy.

In Kansas it is 60 for monthly allowance. NH takes the rest of mom's SS check each month. It used to be 30. STILL...not enough to take her to funerals, activities, to visit realitives, buy her shoes, clothes, bras, pants, etc...NH loses almost everything I buy her and they let her get so soaking wet that she ruins her nice leather shoes that I buy her. I feel like asking them....how does Mom get reimbursed for NEGLECT???

Yes, she gets to keep from $ 30 - 90 a mo for "personal needs allowance" - the amount varies by state. The allowance can either be placed in a trust @ the faciity in which she or family can draw from as needed which usually means her SSDI goes to the facility directly OR you if you have DPOA and are her representative payee can pay the facility from her checking account (that gets the SS deposit) and the personal needs allowance is held back in her account. You are lucky in that most states do NOT have a waiver that allows for AL to be paid this way as most AL is private pay or LTC insurance.

If Sissy has debt (car, mortgage, credit cardsetc), this is going to be issue as she will have no funds to pay basicially for anything but the AL. Good luck

Her monthly living expenses are probably going to be paid by Medicaid, if she has no other source of income except the SSD, and under Medicaid what her check does not cover the government supplements to the facility. She will be left with a small stipend each month for her personal needs, and that is usually somewhere in the $30 to $50 range. If you go to the Social Security and Medicaid websites there is a multitude of information there that will answer all of your questions concerning how this works and give you a better understanding.