I'd second the suggestion to explore having her move in with you. More and more people are giving it a go and finding that while it does have its struggles, with some adjustments it can work out well.
Even a room in a house is usually upwards of $300/month plus utilities. Plus, does she need services to help her manage her disability? Who will be providing those services?
$300/month for housing usually only works if there is a subsidy of some sort such as Section 8 vouchers or tax credit apartments. www.resourcesforseniors.com/pdf/housing.doc
lists various properties with costs and waiting times. Waiting period for a Section 8 voucher can be years.
I'm assuming that she is moving to be closer to you as she ages. If moving in with you is not in the picture, she may want to rethink this moving business. What services/support does she have in place where she is living? Will she be able to access them in this area?
Funding for programs to support those with disabilities is being cut all over the country. For example, if the Texas legislature passes the current budget proposal, Medicaid funding for long term care facilities (already so low that many facilities won't accept it) will be cut by a third in Texas. Yikes!
Sadly, the future does not look rosy for those who depend on financial assistance from the government. I don't know what is to become of those who do not have family who can step in to help.