Here are two links to medical data to explain and support more aggressive B12 levels:

1) http://www.aafp.org/afp/2003/0301/p979.html
This site is for doctors but is written easily enough for laymen to
understand.
It also has data from studies supporting oral use. However, it does not go into empty stomach use, which is very important.
I'd say to get retested in 3 months after 5mg methylcobalamin daily (active form). A good goal for anyone with neuro problems would be 1000 or higher.

2) This is Dr. C. Snow's paper explaining his work with B12 and patients with seemingly "normal" levels who improve with B12 supplements:
http://neurotalk.psychcentral.com/post698522-70.html

Since B12 has no upper limit of toxicity set for it by the FDA, it is something one can take easily without worries about overdosing etc.

This is the B12 thread here:
http://neurotalk.psychcentral.com/thread85103.html

Common OTC drugs for heartburn deplete B12 over time.
Also people with the DNA genetic mutation (10-30% of the US) cannot activate B12 or folic acid properly and then suffer from deficiency in the face of plenty. This polymorphism can be tested for and is called MTHFR DNA test.

I knew an Indian woman whose sister came to US as a vegetarian and was in her 30's. She collapsed one day and ended up in the ER with left sided paralysis/weakness etc.
She was very low in B12 (cultural vegetarian) and with further testing they found she had a heart valve problem, which contributed to the one sided weakness. So keep in mind there could be other reasons for your wife's one sided problems that could be investigated should the B12 intervention not work for her.