The "box" it comes with on the side of the cage has plastic wiered flooring which is unsafe for guinea pigs. The height on the shelf is ok, but instead of buying another expensive pet store cage, you should really invest in a C&C cage where you also can have the room to get her a friend.
Guinea pigs are highly social animals & need a friend of their own kind, your company isn't nearly enough, and nor is the cage for any more than one pig. And in all honesty the cage looks much smaller then the measurements you've stated.
Visit piggyparadise.co.uk, or google her. She will ship C&C cage kits all over the world if you email her. She's in the process of moving so the cages available are quite few. But please contact her instead of getting another pet store cage. Or make one yourself of C&C or alternative materials.