Inappropriate urination can be a symptom of several things not just Kidney Disease.
The only way to tell for sure is a trip to the vet for a Urinalysis preferably by Cystocentesis so the vet can check for bacterial infection or crystals/stones as well as checking the urine specific gravity which is an indicator of kidney function loss.
I would suggest since she is 13 that while you are there to have them run a full blood panel as well, this will check for abnormal values not only relating to the kidneys but will also check values associated with diabetes, pancreas issues, liver disease etc
You can always call the vet and ask if they will allow a payment plan or if they will take a post-dated cheque. Can you borrow from family/friends until payday?
Avoid biting when a simple growl will do
The Spirit Lives As Long As Someone Who Lives Remembers You - Navaho Saying
Vindication ~ For all those pets who became sick or lost their lives from tainted pet food