Actually, if you pay close attention you'll notice that during all the times
Victoria is outside it's either dusk or early dawn. At no time during the
anime do they show her out in broad daylight. Alucard on the otherhand..
There are several chapters in the manga where Victoria can't be in direct
sunlight but Alucard can walk down the streets in broad daylight without
any ill consequences.
(he's not even wearing his big hat... he's
wearing a business suit at the time)