Many of the online learning sites you mention have course demos or free trials. Look at those and the comments about them here in the forums here to help you decide what might work best for your DD.
Art of Problem Solving's Beast Academy doesn't begin until grade 3 and only runs through level 4A so far, and they are book program, but your DD may be more open to books by the time she reaches that level.
You might combine an online learning system with some books and other enrichment activities. I put together a Math Enrichment Family Resource Book for my daughter's school (grades 5 and 6). You can download it as a pdf for free here:
https://sites.google.com/site/polan...o-math-enrichment-family-resource-book-1Many of materials cover early grade levels as well, and a gifted child can quickly reach the point of handling upper elementary-level materials.
You'll find tons of other enrichment resources in the forums here as well.
Good Luck!
