My mother's rent has gone up twice as much, is this legal?

My mother has been in an Assisted Living for 5 years. Her rent has gone up yearly by a minimal percentage. Currently her rent is $1,200 a month. They asked for proof of Social Security which we gave them. Her SS is $1,600 a month. That is all the money she has. They now are trying to raise her rent to $2,695 a month and have given her a pay or quit notice. Is this legal? Is there any recourse?