If you really intend to put her in a larger tank later on anyway, it's fine to go ahead and buy it now. It's really only hatchlings that get freaked out by larger tanks. Yearlings on up are happy to roam around a huge tank at night, as long as you provide adequate hides and cover for them disappear into during the day. Though you might want to err on the side of smaller hides for now, so she feels secure during the transition.