I think that Sam will enjoy returning to Regular School, for the basic reason that she is going through a phase where she seems to really need to feel "normal" and she feels that she is missing out by not going to Regular School.
It remains to be seen whether she really can achieve going to bed and waking up early, and I question whether that is something she has "always wanted to do". I will also miss seeing her as much, since I have to work weekends, but I think she should try it for the last couple of months of the school year. Then if she decides she really wants to continue, she can start again in the fall. Since she is returning to a school she has attended, and she knows many of the girls in her class from Girl Scouts, she should be able to adapt very well.
Frankly, I think she is going to be bored academically, but right now the social aspects of school seem very important to her, so I'll support her in this decision.