there is certainly more water in canned than in dry, so she may be getting enough from there along with the little she does drink.
one of my dogs refuses to drink tap water, so i have a container of rainwater, planted with pond plants to keep the water sweet for him by the front door.
as you have only had her 3 days, she may simply have not settled in enough to act 'normally' yet. by this i mean, does she play much? can you let her off the leash yet?
if not she probably just isnt as thirsty as she would be if she was bombing round like a nutter all day
however if it keeps up, or you are worried, or she is dehydrated (pinch the skin on the scruff into a tent shape, then release, if hydrated it will spring back, if dehydrated it will take some time to return) then i would get her checked out at the vets in case she picked up something from the shelter.