Depending on your budget:

Low Budget:
Find a nice solid object that fits nicely in one hand, with an exposed outer area. eg. Paddle, baseball bat
Take said object to the grocery store.
Pick up a single item, one very cheap, say a single sweet or something.
Act completely normal, as no one can see your object, as it is strapped to your back.
When she starts processing your item, unsheath your object and use it on her head.
When she has had enough of your object and is out cold, proceed to drag her out of the store while grunting and having your object in plain sight of everyone, warning them to keep their distance.

High Budget:
Obtain chloroform.
Use on girl.
Drag out of store.