I'm so sorry to hear your dog is exhibiting these recent symptoms.
There are a variety of factors that could cause her to suddenly lose her sight, and for her eyes to be bright red. Because your dog is a 'senior', it's possible that she's had a 'bleed' in her brain, her blood pressure is too high, or she had a stroke. This could be causing the drooling of thick saliva, and her other symptoms.
A condition called blastomycosis is also possible and this is caused by a systemic fungal disease which invade the dog's system.
"Causes of blindness include severe corneal disease, anterior and/or posterior uveitis, cataracts (white opacity of the lens), retinal inflammation and infection, retinal detachment, glaucoma (sustained elevated pressure within the eye), disease of the optic nerve (nerve that connects the eye to the brain) and visual pathways, and diseases of the occipital cortex (visual center of the brain)." (source: http://www.petplace.com/dogs/blindness-in-dogs/page1.aspx
Because these symptoms came on so suddenly, and your dog is a senior, she needs to be evaluated by a vet, immediately. Bring her to the nearest ER vet center for assessment and treatment, and hopefully, the blindness will not be permanent.
I hope all will be well with your dog.