I also suspect she'll be just fine with the 5 days per week in the school she is already happy at. Just me, but I wouldn't over-think or worry about giving her extra academics at home either - unless she's asking for it and it's fun for both of you. Highly gifted children are going to move forward quickly with their academics in elementary school so even if you put her into 1st grade already working on 3rd grade math or whatever - chances are she's going to get there on her own quickly anyway. We've always just let our kids lead us in terms of outside-of-school enrichment, did what they asked for, rather than focusing on specific academics to get them ahead - and yet they still advanced ahead, because that getting ahead and staying ahead of grade level is really more about ability than how much prep was done at home.
polarbear