Hello Rebecca:
I guess I too have a long torsoed daughter. I added 1.5 inches to my daughter’s fairy tale along with other dressed that require darts. I guess how I’ve handled it is to not add to the bottom, but to splice the pattern at the point from a notch on both sides, front and back, and add the length between the splice. Then I connect the dart lines between the splice making the dart longer. I first had to do this on an old 1960’s simplicity dress pattern and used their shorten/lenghten here lines and if memory serves, that’s where I lengthened. The lengthened darts look perfectly fine and then the points end at the chest/back where they should. By all means, I’m far from a professional. I’m just going off of my own experiences. I’m trying to get all of my pattern fitting knowledge squared away since I’m working on a dress shirt for my husband and he’s way more picky than my dd. If I don’t get this shirt just right he won’t wear it! Good luck!
Rebecca