First you're a customer, and she shouldn't be making comments on your political affiliation. Second she shouldn't be basing them off an assumption.
To demonstrate the problem with her assumption, I honestly couldn't imagine what political parties would be associated with pearls, so I googled it. So far I have five, plus candidiates from several parties wearing them, and there are probably more.
I would mention it to your friend, as it is possible the assistant will make other assumptions that offend customers. It may not be intentional, but she does need to be corrected. Hopefully she only said it because you are on a first name basis, and she isn't doing that to other customers.