Because she knew that Rodolphus removed all security enchantments and wards around the small house to prevent Antonin from knowing he'd been there, Hermione didn't waste a moment once she arrived to put up the most rudimentary and basic protections. All she needed was enough of a warning that she could make her escape. Sealing the house to any but her would take too much energy and time. She would have to make do with little and hope for the best.