Causes of sudden spike in blood pressure

My mother is in her early 50's, she's never smoked, does not drink and does not eat red meat. She has always been very health-conscious and besides a thyroid problem a couple of years ago, she's never been diagnosed with any illnesses. Two months ago, she started feeling weak and disoriented all of a sudden, and it turns out her blood pressure had spiked to the point where she could not get home from a neighbor's house. After a trip to the ER where she got an anti-anxiety pill, she was back to normal for a couple of days. The problem is that this sudden spike in blood pressure keeps coming back, about once a week or so. It seems to always happen in the early evening, especially when she's walking to or from her house, running errands, etc.

I have told her to go see a doctor right away, but she doesn't seem to think there is any reason to get an appointment in a hurry. She wants to wait until after my brother's wedding, which will happen in about 3 weeks. Should I be worried and insist that she goes for a doctor's appointment and tests right away? My mother hates pills and doctors, as she leans towards a "naturalist" view of diet and lifestyle, and I am having a really hard time convincing her that this could be serious. What could be causing this and how serious should she take it?

Thank you very much!