I believe you need to find a way to pay for Sukie's treatments. She is getting older and if you don't do a dental on her....and don't give her fluids when she needs them because she is having renal issues, she is going to get worse, suffer and die. Sorry if that sounds harsh, but it is a reality.
If the BUN is the only thing elevated, you now have a warning sign. Her kidneys are affected. This is why dentals are so important. The infection from bad teeth wears on the internal organs.
I have no idea what your lifestyle is, but if she were my pup, I would be looking at ways to cut something out so I could provide for her.
Good luck to you and Sukie.
Welcome to YT.
Oh...and another thing. The vet may have told you...if not.....ask him what type of food you should feed her. Usually they need a prescription diet for kidney issues.