I honestly cannot understand how she obtained residency without having someone sign that I-864. Even a temporary green-card (I-551) will not be issued without that form.

Either way though, you should be careful because you may have broken the local Section 8 rules; the last thing you want is to get yourself into trouble there.

My last bit of advice is the same as I've said earlier; seek an attorney.

Do whatever it takes to hire one