She should receive the $1200 stimulus payment — unless you declared her as a dependent on YOUR return!
If she filed a tax return it would come in the mail to that address. Can you contact someone there to accept it — or would the post office return it? That would be a real mess because there is no way to get it again –until she files for a credit on her tax return next year!
The other possibility is that if she receives Social Security, she would receive it likely this month around the time of her monthly SS benefits.
One other thought: You can use this like to file her address — the new one — and see if that helps.