Any hairdressers on here? Color Question

I have naturally medium to dark brown hair. I had highlights put in in September. After they grew out a bit I decided to get rid of them and had my hair dyed a shade or two darker than my natural color, which I LOVED (this was December 5th). Now I feel like it completely faded out, the highlights are still gone but otherwise back to my natural color. I'm so annoyed bc I loved it and it lasted like less than 3 weeks.

I know darker colors fade on blonde hair but she said that shouldn't happen to me since I already have dark hair.

Is this normal? FH's coworker's wife did it and gave me an amazing price but I don't know if I should go back to her or spend a little more money for color that is actually going to stay. I don't know if I should say something to her or not.