A ward is a magical defense, which can be used for a variety of causes and effects. A ward is a defense set up by a magic user. There are a variety of different ones. From killing to detection to stopping hostile magic. Wards are weak without a threshold. It is possible though to make a strong ward if there is a strong enough power source like a ley line.

(She can at least open Harry's. Unsure if she can make her own, but if even practitioners can, it seems logical?)