What your aunt is referring to is the water soluble vitamins. This property of the body to “pee out the extra” is when you take excess water soluble vitamins. For example, you can drink 10,000% daily value of Vit. C, but anything over 100-150% is just going to be excreted through urine. Calcium is a mineral, and it is not the same. However, there is a reason that Caltrate, a calcium supplement, is paired with Vit D. The same reason Vit D is added to milk. It works with the body to help aid absorption of calcium. So make sure you get Vit. D milk (the whole stuff, not skim(1%)), or - the body gets Vitamin D through the skin from sunlight. That will help with calcium absorption.

no i dont think so most of the nutrients are absorbed in your digestive system, so unless you have diarreha or something then it might just got “through you”