Same dye, different color?

I just had my hair redyed by the same beautician, using the same dye that I always have her use, and my hair came out a different color from the color it was two months ago when she did it then.  Why?  I am starting to go through menopause, so perhaps hormones caused it?  She is adamant that she did nothing different, and that the color was the same.  But, I could tell that when it set for awhile before washing out, it was a purple color and it's usually a rust color.  The final color this time was purplish gray and usually it's a strawberry blond.  Oh my, what a big disappointment.