Im sorry to hear about your mother.
The fluctuations of her blood pressure certainly are concerning. Given the fact she is on multiple medications and having these rapid swings, I would be concened about other causes of hypertension. These can include things like renal artery stenosis, hyperthyroidism and pheochromocytoma.
A good internal medicine specialist should be able to handle the adjustment of her medications and help screen for other causes of high blood pressure. Also,they are also probably a bit more accessible then her cardiologist.
Hope this is a start.