Not washing eggs before cracking them can feel strange, but in the U.S., USDA guidance specifically says consumers should not wash commercially purchased eggs at home. USDA-graded eggs have already been washed and sanitized during processing under controlled conditions.
Washing them again under the kitchen faucet can actually create a problem. Eggshells are porous, and USDA warns that household washing can allow contaminated water to be drawn through those tiny pores into the egg.
Instead, food-safety authorities recommend focusing on what happens after you handle the eggs. Wash your hands, utensils, counters, and equipment with hot, soapy water before and after they contact raw eggs or foods containing raw egg.
Cracked eggs should generally be discarded, and eggs should remain refrigerated. Cooking them properly is far more important for food safety than rinsing their shells.
There is one important distinction: practices vary internationally and with freshly collected backyard eggs. Commercial eggs are processed differently depending on the country, so advice about washing and refrigeration is not identical everywhere.
So if your sister-in-law is using ordinary refrigerated supermarket eggs in the U.S., not washing them is actually the recommended practice.