Hopefully the referral will help you and Mandy. Just getting the knowledge of what you are dealing with really allows you to make the right decisions. I know that you are frightened of the sedation. They will typically check some blood work to see how she will manage anesthesia. Also, there are some anesthetics that are safer for geriatric dogs that allow them to wake up sooner. Also, know that by going to a vet college, the knowledge they gain from Mandy can and will help other dogs.
Waiting for the diagnostics is difficult and painful. I know you don't want to hear this, but do know that if you don't get the news you want, you will find the strength to accept the diagnosis. As you process this, your body just goes numb, then you put your baby first. Sadly, I know this from dealing with bladder cancer with my sweet girl.
Take it a day at a time. If you are being told that she isn't in pain and suffering, give her love and support. It is so hard to see them sick. Keeping you and Mandy in my prayers.