We do not offer shipping and need the tax rate to reflect our physical location, NOT the customer's billing address

All of the items we sell on our site must be picked up. Most of our sales come from customers who are physically in our studio (in California) when they purchase. 

Recently, a new customer purchased clay from our online store. But her credit card account is still registered with her old address in Salem, MA and her purchase did not add our local tax -- it didn't add any tax. 

I added a Pick Up option to the order options and it seems to add our local tax only if Pick Up is the option chosen, but not if the Shipping option is selected (although we do not offer shipping, and I can't seem to delete this option).

Short of asking her and anyone with an out of state address to choose the Pick Up option, what can I do?