Does this person has the right to be offended?

Does anyone knows what is a game called cards against humanity? If you don't, please research that before answering this question. In a game of cards against humanity, a friend one mine basically finish the sentence "Yeah I killed _______ , how you ask? With an ______." with "The Jews" and "A M16 rifle". An acquaintance found it so amusing that it took a picture of the cards and posted on Facebook.

Long time after, this same acquaintance got extremely offended when I remembered a joke that I did with one of my friends. I said to this friend of mine that he was "so German that it could be in a SS recruitment flyer." This acquaintance said it was extremely racist and made a long speech about how jokes like that are detrimental to society. She was offended because she had German ancestry.

I first felt bad about it but then I started getting little puzzled. Isn't weird someone that does not mind a joke about killing Jewish people but it is super-sensible with jokes about Germany?