I agree with Pip, EVEN MORE, implies that her brother is intelligent, but she is EVEN MORE intelligent. If the brother were not intelligent, it would make more sense to just say, 'She is more intelligent than her brother.' In this case, it's possible that neither one of them are very intelligent.
A turtle is faster than a snail. (neither of them are fast)
A cheetah is even faster than a leopard. (both are fast, but the cheetah is faster)