I wouldn't expect that the three years out consequence would have any impact on current day behavior, especially for an unmotivated rebellious defiant 15yo. While I don't think it is necessarily wrong in philosophy I just don't think it will work.
I have a 13yo and 15yo. If they turn things in late or get poor grades and aren't doing homework - they get immediate consequences. Their 'currency' is technology and internet so I take it and/or block it. The 13yo sometimes has a crazy big tantrum about it but I don't actually need his cooperation so....... it is a good consequence in my house.
Also - if the teachers suggested possible LD's (Learning Disability) I would for sure follow up on that testing. LD's are different from IQ. It is not uncommon for kids with LD's to have higher than average IQ's. LD's are a game changer and if she has one that is unidentified - figuring that out can be a life changer. Her 'symptoms' are not uncommon with various LD's. It is worth the effort to explore that IMO.
I also totally get not always being able to draw the line between codie and parent. I am getting better at drawing that line. If I'm more invested in the process and/or outcome than they are - I'm over the line, if I'm tweaking consequences to assure their success, getting upset with the child complaining about anothers bad behavior (rocking the boat) versus the child with the actual bad behavior - I'm codie. If I'm all worked up and crazy over 'their' problem and they are just like - "yay - you be worried, stressed, and responsible for my outcomes - I'm just going to hang over here and relax." I'm in the wrong hula hoop. I need to re-think my approach. Love and Logic is great for that btw.