Are you going to have a DAS pass, or Genie+? If not, I wouldn't recommend Hollywood Studios, even though I think the theming would appeal to young children more than EPCOT. It has very few rides, so the lines for almost everything will be prohibitively long within the first hour after park opening. (On the other hand, it does have some shows, so if she likes live theater, that might weight in its favor.) If you have one of those "line helpers," though, I think Hollywood Studios would be the way to go.
EPCOT offers more in the way of "anytime attractions" to do in between headliners, but it's also geared more toward "edutainment," which tends to appeal to an older crowd.