Sorry to hear your DD is struggling. I'm not sure I have much advice I can give you, but parts of your post did make me think of some things. Maybe some others will have more advice for you.
It could very well be that your DD had great expectations when she started at her new school and then found out she is still not being challenged. It sounds like she had a nice "honeymoon" period for several months, then realized she was right back in the same situation she was in at her old school. If her old school had interesting options (art/drama, etc) that her new school doesn't have and on top of that she is still bored and under challenged I can see why she would long to be back at her old school. Basically the lesser of two evils - bored with bells and whistles and interesting options or bored with no interesting options. Getting her into some art classes may help with her no longer having those options, but it still doesn't solve the bored part.
I also agree that our children will have to deal with doing rote work, but if this is a gifted school they should know that rote work is toxic and they should know how to deal with gifted kids. One could assume your DD should not be their first student to ever have these issues.
OR....I could also see a different side of this. Maybe she has coasted through school for so long and now this new school IS challenging her. She is so used to things being easy and now that they are more difficult she is doubting herself. This idea could be a real stretch since you say she brings the work home and gets it done quickly, but thought I'd throw it out there anyway.
The stress from your husband's job may or may not be adding to the other issues going on at school - hard to tell.
I think I would ask for more challenging work for her and see if that makes any difference. See if they will drop some of the repetitious rote work if she can show she already knows the material.
Just my thoughts - good luck!
