Since you had already discussed your intention to get your "M" with your wife and were under the impression you had her support I don't see how she could expect you to just drop everything now that she has had a change of heart. That is the reason you discuss choices that could affect you as a couple before taking the next steps like making a payment that may or may not be refundable.

I think you should continue through with the M2 training and assure her that the training, which is completed within a closed course, is completely safe. As others have suggested, take her along to speak to the instructors because it might calm her fears. It might also help when she sees just how passionate you, the other students and the instructors are when it comes to riding. Who knows, she might even want to become a rider herself.

Fortunately I did not have this problem because I had my bike licence for 5 years before I was married. My wife used to ride with me before we had kids, then once we had kids she suggested I take them for rides. My only issues were with parents, mine were not happy about a bike and hers were even less pleased. Over the years they eventually came around and accepted the fact that I ride a bike. I have been riding for over 35 years and it is a very important part of who I am.