What a difficult situation! You are torn between your compassion and your understanding that, at 60, she is unlikely to change a lifelong pattern. It’s unclear whether she is mentally ill or if she is someone who would rather take advantage of others than take care of herself. Either way, by your account, she hasn’t been willing to seek help or to make changes on her own. It’s very, very difficult to take care of people who stubbornly won’t participate in that care.
You can certainly offer her emotional support but I think it would be unwise for you to let her move in — unless you are willing to be taken advantage of for the rest of her life. You could make a list of local resources and phone numbers for her. At this point, she may be incapable of researching that on her own. What she does with the list may give you more information about her state of mind. Will she make some calls or will she look to you to do even that?
Since the only information I have is from your letter, I can’t offer you more than that. However –You need and deserve support and practical advice for dealing with a family member who is chronically ill. I strongly suggest that you contact the local chapter of NAMI (National Alliance on Mental Illness) and attend one of the support groups for family members. Members offer each other support and advice. Chances are that participants will be able to point you to some local services. In addition, consider joining a forum here at PsychCentral to hear how others in a similar position have managed to walk that fine line between being supportive without being enabling.
I wish you well.