On one of the days when dhe is coherent talk her into getting a power of attorney drawn up, unlimited would be best. Once that is done you have unlimited access to her financial transactions. Get a statement from the bank showing she paid rent and that will be enough to challengew the eviction.
Also see if you can get your hands on some mail that was delivered to her at that address. Remember payments or not if you are allowing someone shelter and to receive mail at your address you have de facto consented to them living their regardless of payments or what not.
You are going to have to maintain legal council for this for the power of attorney and I recommend that you keeo that council.