Forgetting her SS#, DOB and phone number. When asked these things she has to read off paper as she started to write them down. Do you think it’s best she see a Geriatric Dr or Neurologist? Which would best to see 1st. If she would need to see both? My understanding of the testing with geriatric Dr, she will not pass the testing phase.
A Neurologist or a Neuropsychologist will do memory testing and make a "diagnosis" based on the results.
Between now and when her appointment in you might also want to make an appointment with an Elder Care Attorney and make sure you have all the paperwork done that needs to be done for when she can no longer make decisions. the fact that she is not Medicare age a consult with the attorney might be needed.
Do you know what she wants as far as End of Life decisions, IV fluids? Tube feeding? CPR? What are the plans if she needs to be placed in a Memory Care facility?
Are either of you Veterans? If so the VA might be of help.
If you want to check out medical practitioners specializing in dementia do check out National Counsel of Certified Dementia Practioners at NCCDP.org or get advice on alz.org online. Best of luck and hope you'll update us. There are examples of tests online if you care to access them. Sometimes dementia can be mimicked by anxiety disorders. Stay hopeful until you know. Glad she is agreeable to testing; that is in fact a POSITIVE sign.
I believe it's good to have a doctor experienced with older patients' issues once we get to a certain age. Although your wife is not old old, she has a problem that a geriatric doctor sees and treats all the time. That doctor can advise. I wish you luck.