Is one of the blood pressure medicines Metoprolo. If so it can cause Diabetes.
I assume since you are giving her B12 that you read that Metformin can cause B12 deficiency. In some countries the lower end of the range (starting point) is 500-550pg/ml this equals 461pmol/l. I say this because in the USA you can have a much lower level and be declared as “fine”.
I read another post that said Metformin can cause CoQ10 and B9 deficiencies.
As for the bullous pemphigoid and Metformin see http://www.sci-rep.com/index.php/scirep/article/view/57/46. Apparently Bullous Pemhigoid can be caused by autoimmune response and non-autoimmune response. I say this because there is a connection between low Vitamin D and autoimmune diseases. There is also a connection to low Vitamin D and low B12. (I do realize her D levels like I said before are at least reasonable.)
Has Mom had her thyroid levels checked recently. At a TSH level of 2.5-3.0 I would be very suspicious of a thyroid problem. There are also other tests that can be done like antibody levels and actually measuring thyroid hormone levels. Hypothyroidism causes increased cholesterol and could eventually lead to diabetes.
As for other tests. I can tell you that ANY mineral test only shows the 1-2% that is in your blood stream and not total body stores. So for example, if they do a blood test for magnesium and it is “in range” you can still be deficient. The only thing you can do is supplement and see if it helps whatever condition or symptom you have.