Hello Mary, I'm Dr. Deb.
I just came online and see that your question about Sandy hasn't been answered. I'm so sorry that you've had to wait for a response,but if you still need assistance, I'd like to help if I can.
The short answer to your question is that, yes, it should be ok to wait to have Sandy seen until tomorrow.
When older dogs develop the symptoms you're seeing (balance issues with a head tilt), then more than likely vestibular issues are going to be the reason why. These issues can involve either the central nervous system (the brain) or the middle/inner ear.
So the possible explanations include:
1. Idiopathic Vestibular Syndrome or also known as Old Dog Vestibular Syndrome. We don't know what causes this condition but these dogs will start to show improvement within three days and are expected to make a full recovery. Some vets treat this condition with steroids but most don't since the dogs will get better on their own. Since the balance is off, it's important to not let Sandy hurt herself and support her as you have been.
2. Inner or middle ear infection. Usually these dogs do have a head tilt in addition to being unbalanced.
Diagnosis is with an MRI or CT scan although if I suspect it, I'll start antibiotics (the treatment for this condition). . Most of these dogs will recover very well although some will have a mild head tilt.3. Unfortunately a brain mass can cause these symptoms. It would also take an MRI to diagnose this condition but obviously the prognosis is not optimistic in most cases even though brain masses tend to be benign and slow growing.
I don't include this possible explanation to be alarming but rather to be complete.
This LINK may be useful in providing additional information about Vestibular Disease in dogs. Some of these dogs can be somewhat nauseous so Dramamine (Dimenhydrinate) can be given at a dose of 4 mg/lb twice a day which can help with this if they are.
I wouldn't consider her symptoms to be a medical emergency especially since she's otherwise acting her normal self so an ER visit today wouldn't be necessary unless the situation changes.
I hope this helps although, again, my apologies for the delayed reply. Deb