I can understand how distressing it is to see your girl acting this way.
What you are describing sound like "geriatric vestibular syndrome" (vestibulitis) which can occur very suddenly, usually in older dogs. There are a couple of other much more rare possibilities (inner ear infection, or a mass in the brain) but the vast majority of dogs with what you are describing will have vestibulitis.
Vestibulitis or geriatric vestibular syndrome is due to an irritation or inflammation of the inner ear, which contains the vesibular apparatus. This is the part of the inner ear that controls balance. It is a bit like an egg, with fluid in it, and little tiny hairs on the inside. When the fluid moves, the little tiny hairs feel that movement and tell the brain "You are moving!" This is good normally. But when the vestibular apparatus tells the brain that there is movement when the eyes are telling the brain that there is NOT, the animal gets horribly dizzy and can't stand up.
It's a bit like spinning around and around and then sitting down suddenly. The fluid in your vestibular apparatus keeps moving but your eyes tell your brain that you are not. You feel dizzy! So, this is the same but worse.
What you saw with your dog's eyes’ moving back and forth rapidly is called "nystagmus" and it is a measure of how fast things are going in that inner ear. No wonder the poor girl had trouble getting up! This is very distressing to dogs, as you can imagine.
You are probably getting very worried about your dog - but there is good news! Vestibulitis usually starts to improve in 72 hours, and resolves entirely in 1-2 weeks. We don't really know what causes it, and don't have any specific treatment to fix it, but it does go away without treatment the vast majority of the time. Some dogs will have a head tilt for the rest of their life, but it doesn't seem to worry them.
So, what can you do for your dog now?
First of all, you will have to assist her to go outside to urinate and defecate this morning. Carry her outside, and hold her to posture while she does her business. This may be easier if you get a big towel, and fold it so it long and thin. You can put this under her belly, and hold the ends above her hips so that you are holding her weight. Also, you can put a second towel under her front end by putting it behind one front leg and in front of the other, so that the towel takes the weight of her chest. This may help you to hold her in position to urinate and defecate.
Next, you are going to need to help her to drink. If you bring the water bowl right up to her head she may be able to get her tongue into it. But in her world that water bowl is spinning like crazy, so she may not be able to! If she can't, then get water into her with a turkey baster. For a dog her size (I'm guessing about 60lbs?) she should drink about 4 cups of water a day. Give that to her by giving her 1/4 cup an hour, trickled slowly into her mouth.
It is probably best to skip breakfast this morning as she is likely to be too dizzy to keep it down. Most dogs get a little better at dealing with this in a day or so. You may find that you need to hand feed her dinner tonight. I usually suggest about 1/4 the normal amount initially. She may find it easier to eat a mixture of 3/4 cooked white rice and 1/4 lean cooked meat (chicken, beef, turkey or even an scrambled egg). HAND FEED her as this is more likely to work.
If you have to go out and leave your girl at any point, leave her in a safe area - NO stairs! She probably just wants to lie still and hope this goes away soon.
Some dogs get really nauseated with geriatric vestibular syndrome. If that happens, you can give her some Gravol or Dramamine (dimenhydrinate). You can find the dose here:
I would suggest you phone your veterinarian when they open to update them on your dog's condition, and they will advise you if they would like to see you.
Let me give you some links to further information:
I will still be here to provide more information if you need it!