In the future, maybe she can agree to let you know in advance of a major cut and indulge you in taking a lot of pictures with her long hair in the days before. It can help with initial period of shock and transition, and she probably would rather you be looking at pictures of her vs internet women.

Also, maybe she'll agree to let you go with her to the salon. Even if you don't enjoy what is happening, you're together, and stylists are much less likely to chop more than requested if someone else is with her.